Viral Therapy of Human Cancers (Basic and Clinical Oncology)

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Author: Joseph G. Sinkovics | Joseph Horvath

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DK1306_half 9/16/04 2:07 PM Page 1

Viral Therapy OF

Human Cancers

DK1306_title 11/19/04 4:04 PM Page 1

Viral Therapy OF

Human Cancers E D I T E D

B Y

Joseph G. Sinkovics University of South Florida College of Medicine Tampa, Florida, U.S.A. University of Texas MD Anderson Cancer Center Houston, Texas, U.S.A.

Joseph C. Horvath St. Joseph’s Hospital Cancer Institute Biotherapy Research Laboratory University of South Florida College of Medicine Tampa, Florida, U.S.A.

MARCEL

MARCEL DEKKER DEKKER

NEW YORK

Although great care has been taken to provide accurate and current information, neither the author(s) nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage, or liability directly or indirectly caused or alleged to be caused by this book. The material contained herein is not intended to provide specific advice or recommendations for any specific situation. Trademark notice: Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress. ISBN: 0-8247-5913-3 This book is printed on acid-free paper. Headquarters Marcel Dekker, 270 Madison Avenue, New York, NY 10016, U.S.A. tel: 212-696-9000; fax: 212-685-4540 Distribution and Customer Service Marcel Dekker, Cimarron Road, Monticello, New York 12701, U.S.A. tel: 800-228-1160; fax: 845-796-1772 World Wide Web http://www.dekker.com The publisher offers discounts on this book when ordered in bulk quantities. For more information, write to Special Sales/Professional Marketing at the headquarters address above. Copyright  2005 by Marcel Dekker. All Rights Reserved. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher. Current printing (last digit): 10 9 8 7 6 5 4 3 2 1 PRINTED IN THE UNITED STATES OF AMERICA

Preface

Could viruses contribute to the cure of cancer? Viruses certainly contributed to the cause of cancer. Retroviruses transduced cellular proto-oncogenes and converted them into oncogenes. Certain DNA viruses knock out the tumor suppressor gene product proteins of p53 and Rb and counteract early apoptotic death of the infected cell, thus eliminating a self-defensive reaction of the infected host, in which these virions or at least their genomes will persist. The infected cells assume transformed or malignant pheno- and genotypes, gain ‘‘immortality’’ and grow as cancers. On the other hand, some naturally acquired virus infections induced remissions in tumor-bearing patients. There are rare but well documented and published records of various human malignancies, more leukemias and lymphomas than other types of cancers, yielding to a natural viral infection and regressing without relapse. In the laboratory, mice and other experimental animals are readily cured of their cancers, ascitic tumors in particular, by direct inoculation of these tumors, or by infection of the animals with some selected viruses that are not pathogenic in these hosts. These ‘‘oncolytic viruses’’ readily kill tissue cultures or xenografts of human cancers. In clinical trials, be as simplistic as letting patients repeatedly drink or intranasally inhale or receive as an enema untitrated veterinary virus preparations, or as sophisticated as the intratumoral injections of a genetically engineered virus, tantalizing, rare, temporary remissions of cancers occur and are lost to relapses. Long stabilizations of the disease are more commonly recorded and are readily attributed to the viral intervention, iii

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disregarding that some advanced tumors can assume a Gompertzian growth curve and slow down their growth rate on their own. Decades go by, but not one particular virus emerges as the ideal oncolytic agent for human tumors. In melanoma, there is a strong claim that oncolysates prepared with Newcastle disease virus eliminated subclinical microscopic disease left behind after surgical removal of gross tumors. Because the Cassel-Murray clinical trial was evaluated against historical controls and was not prospectively randomized, it is not readily accepted as valid. Even though the trial was impeccably carried out for almost two decades, the academic institution (Emory University, Atlanta, GA) keeps accurate records of its patients and tumor-free patients are alive, this claim of successful virotherapy of a highly malignant human cancer is often ignored and dismissed. However, we accepted the curative value of the MOPP regimen for Hodgkin’s disease and that of the first cis-platin, bleomycin and vinblastine protocols for testicular carcinoma without prospectively randomized trials. If it is true that microscopic subclinical cancer can be eradicated by a virus, then it is also possible that resident apathogenic viral flora of the human host (parvoviruses; reoviruses; and as yet undiscovered other viruses) can eliminate incipient newly emerging tumors. Further, if this really could happen, some anti-tumoral immunity should remain in these individuals. We cite not only the surveillance by innate NK cells that kill virally infected cells and tumor cells and respond first to immunizations of patients with viral oncolysates, but also the immune T cells, which arise after the inception of a tumor. If one of us could document immune T memory cells specifically reactive to tumor-associated antigens in a healthy and tumorfree individual who never had any documented cancer before, would this finding be acceptable as a proof for the rejection of an incipient tumor in that individual? It would require a series of additional documentation to establish just how that incipient tumor was rejected; viral attack on that tumor would be one of the possible means of its rejection. In this volume, virologists of the old school meet with the new generation of molecular virologists. Together we try to decipher the controversies embedded in the intricate processes of viral oncolysis, as this discipline of treatment for cancer is applied in preclinical and clinical trials. We are comparing the efficacy of naturally oncolytic and genetically engineered viruses. Gene therapy of cancer has not been reviewed, however, it has not been ignored! It is frequently referred to in this volume. The new generation of virologists persuing

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the virotherapy of human cancer forms a nicely knit cooperative group. They meet, confer and publish together. Here we list just a few of their recent conferences to guide the reader to early abstracts and full reports. A. Cid-Arregui (Heidelberg, Germany) and A. Garcıá-Carranca´ (Ciudad Mexico, Mexico) edited the volume ‘‘Viral Vectors: Basic Science and Gene Therapy’’ published by Bio-Techniques/Eaton (Natick, MA) in 2000. In that volume from adenoviruses to vesicular stomatitis virus all genetically engineered viral agents useful for the viral therapy of cancer are elaborated on. A conference on ‘‘Replicating Vectors for Gene Therapy’’ took place in Rochester, Minnesota on October 5-7, 2001. This conference was organized by the Mayo Clinic and its abstracts are printed in Gene Therapy volume 8, Supplement 1, 2001. The abstracts of the ‘‘Eleventh International Conference on Gene Therapy of Cancer’’ was held on 12-14 December, 2002 in San Diego, California; its abstracts are printed in a special extra volume of Cancer Gene Therapy 2003; 10: S1-S44. Papers on naturally oncolytic and genetically engineered viral vectors were presented at these conferences. Finally, the conference entitled ‘‘Oncolytic Viruses as Cancer Therapeutics’’ was held on March 26-30, 2003 in Banff, Canada, organized by the Ottawa Regional Cancer Centre (www.orcc.on.ca). There, a most spectacular array of presentations took place with the take home message that we do have a new and working weapon against cancer in the form of naturally oncolytic and/or genetically engineered viruses. Will viral therapy of human cancers match or surpass the efficacy of chemoradiotherapy or that of the new biological therapeuticals: gene therapy (T. Wasil and A. Buchbinder), ribozymes (Louise Wright and P. Kearney), or antisense oligonucleotides ( B.P. Monia, J. Holmlund and F.A. Dorr) as reviewed in Cancer Investigation (Marcel Dekker) volumes 18-9, 2000-1. Is viral therapy of human cancers a collaborator or a competitor of tyrosine kinase inhibitors targeting oncogene cascades or that of cancer vaccines or monoclonal antibodies/immunotoxins? Would sensational announcements of success with virotherapy of cancer (T. Pawlik and K. Tanabe inducing death of colon carcinoma cells with Herpes simplex virus mutant rRp450 and using it with cyclophosphamide and ganciclovir for the treatment of liver metastases) translate for therapy and withstand the tear and wear of late relapses (Oncology News International, June, 2000). It is a privilege for us to serve as editors of a volume on virotherapy of cancer. In this volume, we present virotherapy of cancer in context, that is, how it is related to work done along these lines decades ago and how it is comparable with other biological thera-

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peuticals now in clinical trials. The abundance of choices is overwhelming. Close to innumerable adenoviral vectors populate the field. We could have catalogued or tabulated them giving each item one line. Instead, one of us (JGS) condensed each of them in a sentence or two with a reference. Enough information is given to the reader to locate the viral vector of interest in the computer or in the library. There is a saying in medical oncology: ‘‘if a tumor category is being treated with more than five regimens, that means none of them is working’’. Hopefully, this dictum is not applicable to the rapidly proliferating adenoviral vectors. Each of them is the result of superb basic knowledge of tumor cell biology and congenial thinking; each of them deserved to be cited. One of us (JGS) expresses his gratitude to Dr. Robert W. Simpson, emeritus professor of virology, The State University, Rutgers, The Waksman Institute, New Brunswick and Piscataway, New Jersey, and to Dr. H. David Kay, virologist, immunologist and patent attorney formerly affiliated with The University of Texas M. D. Anderson Hospital, Houston, Texas, and with The University Medical School, Omaha, Nebraska for reading and criticizing the JGS manuscripts. While this volume was edited, The U.S.A. Department of Agriculture launched an investigation on all Newcastle disease virus strains used for research and vaccination to find out if these virus strains posed any biohazard to wild and domesticated birds, especially poultry, and to human beings. One of us (JCH) had to turn his full attention toward cloning and sequencing part of the genome of the 73T Newcastle disease virus strain with which we prepare our viral oncolysates for immunization of patients. However, the virus turned out to be not viscerotropic and it poses no biohazards in the human community or in the ecosystems in which we live. Our work at Emory University (Atlanta, GA) with this virus may continue unimpeded. We regret the delays this publication had to sustain. Nevertheless, we proudly present to the readers some magnificent articles on viral oncolysis and are very grateful to the authors for their contributions. In the chapter on biological therapy of cancer, one of us (JGS) frequently mentions (in parentheses) drug companies and laboratories sponsoring research on this subject matter. This is done to assist the interested reader to locate better the source of information and facilitate making contact with the manufacturer of a new investigational product. Here we, the editors of this volume, explicitly declare that neither one of us received any monetary rewards or presents

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from any one of the cited (or non-cited) drug companies or research laboratories. The contributing authors were given unrestricted liberty as to the construction of their chapters and as to their choices for literature citations. Since we could not engage Dr. Patrick Lee for a reovirus chapter, we asked Drs. M. Bergmann and T. Muster to include a review of oncolytic reoviruses into their chapter. Who could have contributed better than the P.W.K Lee team [1]? After CRC Press and Marcel Dekker publishers united, we had the good fortune to have the assignment of Ms Kathryn Phillips of Maryland Composition as project manager to take charge of the accelerated publication of this volume. Ms Phillips removed all elements of stagnation and acted with care and expertise. We wish to express our gratitude for her efficient interventions. We hope that we have rendered a useful service for those who work in the laboratories or conduct clinical research on the virotherapy of human cancers; to the medical oncologists in practice; and to those patients who are in need of innovative new treatment modalities. Joseph C. Horvath, M.D and Joseph G. Sinkovics M.D.

1. Norman KL, Farassati F, Lee FWK. Oncolytic viruses and cancer therapy. Cytokine Growth Factor Rev 2001;12:271–282.

Contents

Preface Contributors 1. Progressive Development of Viral Therapy of Human Cancers: A Personal Narrative Account Joseph G. Sinkovics 2. New Biological Therapeutics: Competitors or Collaborators of Viral Therapy for Human Cancers Joseph G. Sinkovics 3. Measles Virus: Improving Natural Oncolytic Properties by Genetic Engineering Christoph Springfeld, Adele Fielding, Kah-Whye Peng, Eva Galanis, Stephen J. Russell, and Roberto Cattaneo 4. Antitumor Immune Memory and its Activation for Control of Residual Tumor Cells and Improvement of Patient Survival: A New Concept Derived from Translational Research with the Virus-Modified Tumor Vaccine ATV-NDV Volker Schirrmacher

iii xi 1

149

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481 ix

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Contents

5. Newcastle Disease Virus: Its Oncolytic Properties Joseph C. Horvath 6. Influenza A Viruses with Deletions in the NS1 Gene—a Rational Approach to Develop Oncolytic Viruses Michael Bergmann and Thomas Muster 7. Vesicular Stomatitis: an Oncolytic Virus that Exploits Tumor-Specific Defects in the Interferon Pathway Rebecca Ann C. Taylor, Jennifer M. Paterson, and John C. Bell 8. Parvoviruses As Anti-Cancer Agents Jean Rommelaere, Nathalia Giese, Celina Cziepluch, and Jan J. Cornelis 9. Newcastle Disease Virus Oncolysate in the Management of Stage III Malignant Melanoma William A. Cassel, Douglas R. Murray, and Zbigniew L. Olkowski

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575

597

627

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10. Vaccinia Viral Lysates in Immunotherapy Of Melanoma Peter Hersey

691

11. Fusogenic Oncolytic Herpes Simplex Viruses for Therapy of Solid Tumors Xinping Fu, Mikihito Nakamori, and Xiaoliu Zhang

713

12. Poliovirus Recombinants Against Malignant Glioma Melinda Merrill, David Solecki, and Matthias Gromeier

739

13. Oncolytic Viruses that Depend on Loss of RB or p53 Frank McCormick

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Epilogue: ‘‘Damn the Torpedoes! Full Speed Ahead!’’ Joseph G. Sinkovics and Joseph C. Horvath

797

Index

813

Contributors

John C. Bell Ottawa Regional Cancer Centre Research Laboratories, Ottawa, Ontario, Canada Michael Bergmann Department of Surgery, University of Vienna Medical School, Vienna, Austria William A. Cassel Emory University School of Medicine, Atlanta, Georgia Roberto Cattaneo Molecular Medicine Program, Mayo Clinic Rochester, Rochester, Minnesota Jan J. Cornelis Applied Tumor Virology Program (Abteilung F0100 and Institut National de la Sante´ et de la Recherche Me´dicale U375), Deutsches Krebsforschungszentrum, Heidelberg, Germany Celina Cziepluch Applied Tumor Virology Program (Abteilung F0100 and Institut National de la Sante´ et de la Recherche Me´dicale U375), Deutsches Krebsforschungszentrum, Heidelberg, Germany Adele Fielding Molecular Medicine Program, Mayo Clinic Rochester, Rochester, Minnesota xi

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Contributors

Xinping Fu Center for Cell and Gene Therapy, Departments of Pediatrics, Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas Eva Galanis Molecular Medicine Program, Mayo Clinic Rochester, Rochester, Minnesota Nathalia Giese Applied Tumor Virology Program (Abteilung F0100 and Institut National de la Sante´ et de la Recherche Me´dicale U375), Deutsches Krebsforschungszentrum, Heidelberg, Germany Matthias Gromeier Department of Molecular Genetics & Microbiology, Duke University Medical Center, Durham, North Carolina Peter Hersey Oncology & Immunology Unit, Newcastle, NSW, Australia Joseph C. Horvath St. Joseph’s Hospital Cancer Institute Biotherapy Research Laboratory, University of South Florida College of Medicine, Department of Medical Microbiology & Immunology, Tampa, Florida Frank McCormick University of California-San Francisco Cancer Research Institute, San Francisco, California Melinda Merrill Department of Molecular Genetics & Microbiology, Duke University Medical Center, Durham, North Carolina Douglas R. Murray Emory University School of Medicine, Atlanta, Georgia Thomas Muster Department of Dermatology, University of Vienna Medical School, Vienna, Austria Mikihito Nakamori Center for Cell and Gene Therapy, Departments of Pediatrics, Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas Zbigniew L. Olkowski† Emory University School of Medicine, Atlanta, Georgia

†

Deceased.

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Jennifer M. Paterson Ottawa Regional Cancer Centre Research Laboratories, Ottawa, Ontario, Canada Kah-Whye Peng Molecular Medicine Program, Mayo Clinic Rochester, Rochester, Minnesota Jean Rommelaere Applied Tumor Virology Program (Abteilung F0100 and Institut National de la Sante´ et de la Recherche Me´dicale U375), Deutsches Krebsforschungszentrum, Heidelberg, Germany Stephen J. Russell Molecular Medicine Program, Mayo Clinic Rochester, Rochester, Minnesota Volker Schirrmacher Division of Cellular Immunology, Tumor Immunology Program, German Cancer Research Center (DKFZ), Heidelberg, Germany Joseph G. Sinkovics Cancer Institute, St. Joseph’s Hospital; Departments of Medicine and Medical Microbiology-Immunology, The University of South Florida College of Medicine; The H. Lee Moffitt Cancer Center, Tampa, Florida David Solecki Department of Developmental Neurobiology, Rockefeller University, New York, New York Christoph Springfeld Molecular Medicine Program, Mayo Clinic Rochester, Rochester, Minnesota Rebecca Ann C. Taylor Ottawa Regional Cancer Centre Research Laboratories, Ottawa, Ontario, Canada Xiaoliu Zhang Center for Cell and Gene Therapy, Departments of Pediatrics, Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas

1 Progressive Development of Viral Therapy of Human Cancers A PERSONAL NARRATIVE ACCOUNT

JOSEPH G. SINKOVICS Cancer Institute, St. Joseph’s Hospital; Departments of Medicine and Medical Microbiology–Immunology, The University of South Florida College of Medicine; and The H. Lee Moffitt Cancer Center Tampa, FL

EARLY HISTORY In 1893, the Hungarian physician F. Kovaćs, practicing in Vienna, Austria [1], observed remissions in leukemic patients after natural infections. Viral infections? Perhaps, but only by exclusion. The diagnosis of bacterial infections must have been fairly well established by then and in the absence of a bacterial 1

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pathogen, viral infection could have been suspected. Kovaćs mentions ‘‘Influenza,’’ ‘‘Herpes,’’ and ‘‘Morbilli’’ in his paper, but these were clinical diagnoses at the best; those viruses were not isolated and identified until many decades later. Indeed he does not mention the word Virusarten because that word probably did not exist in the medical vocabulary at that time. Leukemia as wei␤es Blut was well described by Virchow in the mid-1800s and Lo¨ffler & Frosch discovered the causative virus of foot and mouth disease in 1898. Therefore, it must not have been possible to readily diagnose and prove human viral diseases as early as in the last decade of the nineteenth century. G. Dock is credited as being the first to realize that coincidental viral infections can ameliorate the clinical course of human leukemia [2]: A woman with ‘‘myelogenous leukemia’’ and hepatosplenomegaly contracted ‘‘influenza’’ with a reduction of her leukocyte count from 367,070 to 4,775 and diminishing hepatosplenomegaly; her remission lasted more than 6 months. Subsequently, in 1964, E. F. Wheelock* and J. H. Dingle, working at the Cleveland Research Center of the University Hospital, Cleveland, OH, inoculated influenza A and B, Newcastle disease and arboviruses into a patient with acute myelogenous leukemia and recorded repeated partial remissions of the disease that eventually terminated in death [3]. In 1910, an Italian woman was suffering from carcinoma of the uterine cervix. Her case history was presented that year at the International Cancer Conference in Paris, France. After an accidental exposure to lyssa, she received the attenuated live rabies (Pasteur-Roux) vaccine. Her enormously large vegetating tumors unexpectedly regressed [4]. The author, N. G. De Pace, gave the patient 30 injections of emulsione di midollo rabido attenuato secondo il metodo di Pasteur and clearly recognized that il virus rabido eliminated all gross remnants of *

Dr. E. F. Wheelock is the discoverer of gamma interferon (IFN␥); when he moved to The University of Texas at Galveston to chair the Microbiology Department, this author had the privilege to meet him on several occasions for discussions on matters of mutual interest.

Progressive Development of Viral Therapy

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the tumors (l’eliminazione di grossi pezzi di tumore) due to cytolysis un’azione citolitica sulle cellule neoplastiche. One wonders whether the regressing tumor contained bona fide Negri inclusions? Thereafter, in the 1940s, G. T. Pack in New York City used the live attenuated rabies vaccine to treat patients with metastatic melanoma [5,6]. He reported the first remissions ever induced in that malignancy! After these spectacular remissions received extraordinary publicity and posed unrealistic demands for this modality of treatment, most of the patients relapsed. Unfortunately, virus therapy of melanoma was then abandoned. Virus therapy of human tumors was resumed again worldwide in the 1950s and 1960s—in the United States, England, Latvia, the Soviet Union, and Japan; in the late 1970s in China; and in the late 1980s in Germany and Hungary (literature cited) [7–14]. However, this modality of treatment could not advance to the accepted rank of a proven, effective, and established therapeutic modality. None of the real pioneers took out a patent on the virus therapy of human cancers (as Albert Sabin did not patent his polio vaccine and Cesar Milstein and Georg Ko¨hler did not patent monoclonal antibodies). There are fascinating similarities regarding the histories for virus therapy of human cancers and virus therapy of bacterial infections. Bacteriophages have evolved by recombination and chimerism. Thus, derivatives of some of their ancient genes have reappeared in adeno- or reoviruses. Phage ⌽6 may be a possible ancestor of retroviruses. The latent state of lysogenic prophages resembles that of the retro-provirus, which is reversely transcribed and vertically transmitted as retroviral RNA → DNA sequences inserted in the genome of their host cells. Phages may acquire host cell genes that enable them to encode bacterial toxins (example: the 933W ␭ coliphage encoding Shiga toxin), whereas retroviruses can transduce cellular proto-oncogenes. The estimated biomass of phages is 10% or more of that of the prokaryotes populating the Earth [15]. After the discovery of bacteriophages at the Pasteur Institute in Paris in 1917, Felix d’Herelle and his colleagues in

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France successfully treated bacterial infections in children and adults using phage preparations. Eli Lilly in the United States produced therapeutic ‘‘phage preparations’’ in the 1940s. The Eliava Institute in Tbilisi, Georgia, in the Soviet Union, mass produced and distributed phage preparations in alliance with d’Herelle. Then disastrous events occurred: These efforts received adverse criticism. Two articles in the United States described bacteriophages as ‘‘inanimate enzymes’’ and the work with them was declared to be unscientific, with grossly exaggerated results. There was a lack of control groups (no prospectively randomized trials; ‘‘low priority,’’ some wise project site visitors would say today); Giorgi Eliava was executed by the KGB; d’Herelle died; and the original crude phage preparations were found to have contained bacterial toxins [16] (maybe inadvertently combining phage therapy with Coleys ’s bacterial toxin therapy). Thereafter, the discovery of antibiotics rendered ‘‘phage therapy’’ unnecessary. However, multiple drug-resistant microbes emerged and perpetuated their antibiotic-resistance plasmids to each other. Suddenly it was rediscovered (and publicized by the media) that the Eliava Institute still manufactures therapeutic phage preparations and that in Wroclav, Poland (formerly Breslau, Germany) at the Hirszfeld Institute of Immunology, a branch of the Polish Academy of Sciences, there still is an active pursuit of clinical research in ‘‘phage therapy’’ for veterinary and human bacterial infections. Currently there is access to phage preparations against all common and uncommon bacterial infections, including the Mycobacteria of tuberculosis, vancomycin-resistant Enterococcus faecium, and methicillin-resistant Staphylococcus aureus; Serratia endocarditis; and for infectious complications (including Salmonella and Bacteroides septicemias) in cancer patients [17–32]. There is even ‘‘a bacteriolytic agent that detects and kills Bacillus anthracis’’ and Nature publishes an editorial entitled ‘‘Virus Deals Anthrax a Killer Blow’’ [33,34]. There are no harmful side effects of properly purified new phage preparations, but antibodies of the host may neutralize


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the virus after repeated inoculations of the same phage preparation. However, by serial passages of virulent phages, subclones of the virus may be selected out that are less immunogenic [35,36]. In bacteria, natural killer genes exist that can eliminate plasmid-free individual cells in a process resembling programmed cell death. Genetically engineered non-lytic phages could deliver such killer genes (the gef genes in the M13 phagemid system) into bacterial cells. Pseudomonas aeruginosa, a major pathogen in cancer patients, is very sensitive to gef gene-mediated killing [37]. In comparison, virus therapy of cancer is an approach that was also repeatedly initiated and abandoned. Its value has been (and sometimes still is) grossly exaggerated (and publicized in the media) or completely denied. It received no academic credentials. It was not supported by the National Institutes of Health/National Cancer Institute (NIH/NCI). Antibody production of the host was believed to have hampered its efficacy. Cancer chemotherapy rendered it unnecessary, but as cancer cells gained multiple drug-resistance, it has been re-enlisted to take its place among the new biological treatment modalities. A possible caveat is forming: Because P-glycoprotein-overexpressing multidrug-resistant tumor cells do not admit hydrophobic peptides and eject drugs through efflux mechanisms, they also resist infection with enveloped viruses (influenza virus fusion protein) [38]. Nevertheless, oncolytic viruses re-emerge now as their potential efficacy is supported by evidence gathered from molecular virology–immunology and from new controlled clinical trials. In addition to naturally oncolytic viruses, genetically engineered viruses can deliver apoptosis-inducer suicide genes into cancer cells [39–43]. The transduction efficiency of filamentous phagemid vectors recently developed for gene delivery to mammalian cells now reaches 45%. These vectors of low immunogenicity operate with a mammalian reporter gene and express a cell-targeting ligand that confers assured specificity for a cell surface receptor [44]. By the 1950s, the diagnosis of natural human viral infections had become greatly improved. Case reports of children

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with natural varicella or measles infections whose documented coexisting malignancies (acute leukemia, Hodgkin’s disease, Burkitt’s lymphoma) rapidly entered remissions appeared in succession in the literature [45–52]. Adult patients with chronic lymphocytic leukemia received vaccinia virus for vaccination against small pox (variola) (a procedure forbidden in this clinical setting) and remission of the leukemia ensued [53,54]. Other patients with Hodgkin’s disease receiving live attenuated yellow fever (Theiler’s) vaccine experienced remissions. In patients with Hodgkin’s disease, hepatitis A viral infections coincided with some temporary remissions and an amelioration of the clinical course for these neoplasms [55]. Patients with acute leukemia acquiring infection with hepatitis A virus were observed to experience higher chemotherapyinduced remission rates and longer remission durations than similarly treated leukemic patients who were exempt from this viral infection [56,57]. All these remissions are known from brief but documented and published case reports. However, the case of the most popular and most frequently cited Hungarian poultry farmer remains (in the new document-based medicine) an anecdote: He has no name, no hospital chart, no pathological diagnosis, and no tissue sections on which a diagnosis of cancer could be based. Even the year of his alleged recovery from alleged disseminated stomach cancer during an alleged epidemic of fowl plague (Newcastle disease virus; NDV) outbreak in Hungary remains uncertain (unless his factual case history could be located) [58–61]. VIRUSES INTERACT In 2001, it was observed that in human immunodeficiency virus (HIV)-1–infected patients harboring hepatitis G viral coinfection, acquired immunodeficiency syndrome (AIDS) ran a milder and slower course [62,63]. Viruses obviously interact with each other through the modulation of their hosts. Some unconventional practitioners, in order to induce interferon production, treated genital herpes viral infections in homosex-


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ual men using live attenuated poliovirus vaccines grown in monkey kidney cell cultures (prior to the availability of interferon-a or acyclovir). These practitioners were soon falsely accused to have initiated the AIDS epidemic in the Western hemisphere by inadvertently infecting their patients with a simian immunodeficiency virus thought to be the predecessor of HIV-1. Subsequent work established that both Koprowski’s and Sabin’s polio vaccines were free of (did not contain) a preHIV-1 simian virus [64,65]. Some aspersions are still cast on these vaccines (that saved so many lives) because the early Salk and Sabin polio vaccines harbored simian vacuolating virus-40 (SV40), a recognized oncogenic DNA virus. The presence of SV40 DNA sequences or structural proteins in some human tumors (mesothelioma, osteogenic sarcoma, medulloblastoma, thyroid and other carcinomas) strengthens the argument for a viral cause of at least some human tumors, even though the prevalence of SV40 infection in the human population is not known, except that geographic differences that exist are attributed to the type of polio vaccines used [66,67]. Human T cell leukemia virus-I (HTLV-I) causes human lymphoma-leukemia [68], and its xenografted tumors in SCID mice are inhibited by Bay 11-7082 (Calbiochem, La Jolla, CA), an inhibitor of I␬B␣ phosphorylation and translocation of NF␬B into the nucleus, whereby treated tumor cells die apoptotic deaths [69]. Mouse mammary tumor-related retroviral agent is detectable in some cases of human breast carcinoma [70–72]. Epstein-Barr virus (EBV) and human herpes virus type 8 (HHV-8) certainly contribute to the malignant transformation of human lymphoid or endothelial cells, respectively [73–76]. One can also ask whether the Jamestown Canyon virus is a passenger or an etiologically involved agent in human colon carcinomas [77]. These are examples of tumors which, when superinfected with another virus (harmless in the host), might regress owing to viral interference or other related mechanisms, such as certain virally induced cytokines. Three years after its first isolation (1953), an adenovirus strain was already shown to replicate and cause cytopathic

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effects with tumor regression in uterine cervical carcinoma [78,79]. Newcastle disease virus achieved the same effect [10]. Human papilloma virus (HPV)-induced squamous cell carcinomas of the uterine cervix may be unusually sensitive to another viral infection. Instead of viral interference, the doubly infected cancer cells die. This is the tumor that regressed in the Italian woman after vaccination with live attenuated lyssa virus (vide supra). In this entity, HPV E6 and E7 genes surrender the p110RB and the p53 proteins to the ubiquitin-proteasome system for degradation (anti-apoptotic events) to secure tumor cell survival. In contrast, viral gene product structural proteins expressed in the tumor cells induce antibody- and T cell-mediated immune reactions against the HPV-transformed cells [80,81]. The alphavirus Semliki Forest virus (SFV) can be genetically engineered to express a fusion protein from HPV gene product proteins E6 and E7. The SFV-enhE6, 7 construct induces strong antibody and immune T cell responses against the fusion oncoprotein in immunized hosts, whereas in mice it protects against xenografts of human squamous cell carcinoma of the uterine cervix [82]. Nonstructural regions of the viral genome induce apoptosis in human cancer cells even when p53 is deleted. Recombinant replication-defective SFV strains can deliver the IL-12 gene, or the GM-CSF gene or the endostatin gene, into human tumor cells to attract dendritic cells to, and to inhibit neovascularization within, the tumor bed, respectively [83–87]. Another alphavirus of the Togaviridae family, the Sindbis virus, attaches to the 67-kDa laminin receptors of its host cells. Tumor cells overexpress laminins and are readily targeted by the virus and succumb to apoptotic death upon viral entry. This virus has no nuclear phase in its replicative cycle and cannot integrate into the genome of the infected cells [88]. Another alphavirus, Venezuelan equine encephalitis virus, when used as a viral replicon, carrying the HPV E7 gene, induces strong CD8 T cell-mediated immunity against HPV-induced tumors [89]. Additionally, humans harbor highly prevalent, nonenveloped, small circular ssDNA TT miniviruses, members of the families Circo-, Circino- or Para-circinoviridae, that coevolved


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with their hosts through primate speciation in Africa [90]. It is entirely unknown what interaction, if any, these resident viral populations have with naturally infectious or therapeutically inoculated oncolytic viruses. The prevalence of TT viruses ranges from 18% in Europe to 50% in Asia and 70% in Africa and South America [91]. TT viruses are subject to exacerbations in patients with organ transplants, hepatitis, leukemias, and other neoplasms. Are we transferring TT viruses into our tumor tissue cultures or xenografts when we test them for viral oncolysis? FROM MICE TO MAN Returning to the past, in the 1920s, laboratory models of viral oncolysis were set in motion in Paris, France, reaching rapidly spectacular conclusions. Levaditi and Nicolau cured malignant tumors in mice by infecting the tumor-bearing animals or the tumors directly with viruses having no, or limited, pathogenicity in these hosts. Vaccinia, ectromelia and fowl plague (probably ‘‘classical’’ fowl plague and not the later-discovered Newcastle disease) viruses excelled most in their oncolytic activities. Levaditi exclaimed: ‘‘le tumeur fait fonction d’eponge!’’ [92–94]. Alice Moore* at the Sloan-Kettering Institute in New York City confirmed and extended these experimental studies on viral oncolysis [95,96]. Her work gave the impetus for Chester Southam’s* clinical trials for the ‘‘virus therapy of human cancers’’ conducted in the 1950s with arboviruses of African origin (West Nile; Egypt 101 viruses) [97,98]. When their clinical results were presented in 1957 at M. D. Anderson Hospital in Houston, TX, Albert Sabin* pressed for the details. The investigators had to admit that the tumors regrew after the initial virally induced partial remissions were obtained. Sabin concluded: ‘‘Dr. Moore mentioned some very disappointing aspects of the possible use of viruses as oncolytic agents in human *

The author had the privilege to repeatedly visit with the Sloan-Kettering team of virologists, including Dr. Charlotte Friend in 1957 in New York City, and Dr. A. Sabin in Cincinnati, OH, in 1960–1961.

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beings. The most disappointing aspect is the fact that even when a virus is oncolytic and it punches a hole in a tumor the immune response of the individual to the virus occurs so fast that the effects are quickly wiped out and the tumor continues to grow’’ [99]. In this early period, other disquieting reports emerged: One observer described a phenomenon as if rabies and yellow fever viruses enhanced the growth of squamous cell carcinoma explants deriving from the hard palate of a patient, whereas influenza A, St. Louis and Western equine encephalitis (WEE) viruses destroyed these explants. However, the influenza A and WEE viruses were ineffective in halting tumor growth after intratumoral injections in the patient [100,101]. Thus, there was no impetus or convincing evidence to support expections of cures from the virus therapy of human cancers at that time. POSTONCOLYTIC ANTITUMOR IMMUNITY Still in the 1950s, J. Lindenmann and P. Klein [102,103], W. W. Ackerman and H. Kurtz [104], A. D. Flanagan et al [105], and W. Cassel and R. E. Garrett [106] cured ascitic mouse tumors with orthomyxo- and paramyxo- (influenza and Newcastle disease) viruses. At this time, working at the State Institute of Public Health in Budapest, Hungary, I gained my first experience with the oncostatic–oncolytic effects of NDV on Ehrlich ascites carcinoma cells in mice. These NDV strains isolated by us from cases of human oculoglandular illness (vide infra) were adapted to newborn mice. Professors R. Doerr and C. Hallauer in Switzerland welcomed the manuscript and subsequently published it in the Archiv fu¨r die gesamte Virusforschung in 1957 (with more than 1-year delay due to the events of the heroic Hungarian uprising of 1956) [107]. In the meantime, in my textbook of virology, Die Grundlagen der Virusforschung (Hungarian Academy of Sciences, Budapest, 1956), I reviewed all known examples of viral interference and viral oncolysis [9,108]. The work on the full or incomplete replicative cycles of NDV in the mouse brain


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or in mouse tumors and the relationship (or differences) between mumps virus and NDV constituted the subject matter of my first lectures in the United States in 1957, at Vincent Groupe´’s Department of Virology, Waksman Institute, Rutgers University, New Brunswick, NJ; at the Veterinary Medical School, University of Illinois, Urbana, IL; at Jerome Syverton’s Department of Virology at the University of Minnesota’s medical school in Minneapolis; and at the annual meeting of the American Microbiological Society (as published in abstract form in the Bacteriological Proceedings in 1957) (references cited) [109,110]. Much later, in our (Harris JE, Sinkovics JG, authors) monograph: ‘‘The Immunology of Malignant Disease,’’ Second Edition, published in 1976 by C.V. Mosby, St. Louis, MO, I listed many more examples of viral oncolysis [111]. Especially impressive was the oncolytic efficacy of bovine enterovirus-1, regarding which three articles are quoted in that chapter; it remains entirely unexplained why no reports on human clinical trials followed. Regression of virally infected ascitic murine tumors was not a simple matter of viral oncolysis. When mice rendered tumor-free by viral oncolysis were challenged with inocula of the same strain of tumor cells but without further admixture or administration of the virus, there were no takes! These animals had acquired solid antitumor immunity following viral oncolysis (Lindenmann et al; H. Koprowski et al) [102,103,112]. In those years of labile and rapidly and repeatedly revised tenets of tumor immunology, we misinterpreted a single similar experiment. We attributed the ‘‘no takes’’ response to challenge with tumor cells to the effect of a second episode of viral oncolysis by the virus (NDV) latently persisting in the host. In overlooking antitumor host immunity developing consequentially to viral oncolysis, we missed the great opportunity to contribute to the discovery of the phenomenon now known as postoncolytic antitumor immunity. Postoncolytic antitumor immunity is not limited to oncolysis mediated by RNA viruses. The HF10 derivative of herpes simplex virus1 (HSV-1) with deletions of a 3.9 kilobase pair (kbp) at the right end and a 2.3 kbp at the left end of its UL and UL/IRL

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junction in its genome destroys intraperitoneal neoplasms of immunocompetent mice. When these animals are challenged with the same but virus-free tumor cells, they reject these tumor cells [113]. Studies on viral oncolysis of ascitic tumors have produced some discrepancies concerning the results of laboratory assays and clinical trials. According to one statement, ‘‘the most effective viruses were Bunyamwera and Egypt 101, which caused all tumors to regress with survival of the animals’’ [95]. In another laboratory, Bunyamwera virus killed the ascites tumor-bearing mice [112] and Egypt 101 (and other African viruses; for example, the highly oncolytic Rift Valley fever virus) [114] failed to induce durable remissions when administered to tumor-bearing patients [7]. The dsRNA Bunyamwera virus activates protein kinase R (PKR), but it is its nonstructural (NS) protein acting as a virulence factor that blocks interferon production [115]. The NDV strain used at Sloan-Kettering inhibited the growth of murine ascites tumors, but without viral replication occurring in the tumor cells [94,95], whereas other NDV strains replicate in, and kill, Ehrlich ascites carcinoma cells [105,107]. VIRAL ONCOLYSATES More than 10 years later, this notable phenomenon induced us and William Cassel to be the first to prepare ‘‘viral oncolysates’’ (VO) for the active tumor-specific immunotherapy of human tumors. Sinkovics used the PR8 influenza A virus for the treatment of patients with sarcoma and melanoma at M. D. Anderson Hospital in Houston, TX, in 1972–1973 and thereafter (references cited) [116–120]; W. Cassel and D. R. Murray used the live 73T strain of NDV for the treatment of patients with melanoma at Emory University in Atlanta, GA, in 1973 and thereafter [121,122]. Later, M.K. Wallack and H. Koprowski used vaccinia virus for the treatment of patients with melanoma (and patented the procedure; something that neither Cassel nor I ventured to do) at the Wistar Institute in Philadelphia, PA, in 1977 and thereafter [123]; and V. Schirrmacher


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used the Ulster strain of live NDV for the treatment of patients with a large variety of tumors at the Krebsforschungszentrum in Heidelberg, Germany, from the mid-1980s [124] until the present time (see V. Schirrmacher, in this volume). Active tumor-specific immunotherapy with VO for gynecologic tumors continued until recently at the M.D. Anderson Cancer Center in Houston, TX, by R. Freedman, J. Bowen, and C. Ioannides (references cited) [119]. W. Cassel, Z. I. Olkowski, and D. R. Murray have submitted a report for this volume (see Chapter 9) on their 20 years follow-up of their patients with melanomas metastatic to regional lymph nodes and immunized (after surgical removal of gross tumors) with live 73T NDV oncolysates; at 10 years after surgery, more than 60% remained tumor free, in contrast to 15% tumor-free survival of surgically treated contemporary (not prospectively randomized) historical control patients [122]. The Surveillance Committee at M. D. Anderson Hospital in the early 1960s was more lenient than the Institutional Review Boards and the regulatory committees for investigational protocols of the NCI and the Food and Drug Administration are now. I was allowed to register, among others, the following human clinical research projects at M. D. Anderson Hospital: J. G. Sinkovics: Project M27 gm/13: Effect of Oncolytic Viruses in Selected Cases of Human Malignant Diseases (1966-) and Project M27/gm 15: Immunotherapy of Cancer by Immunization with Cultured Tumor Cells (1967-). Beginning in the early 1970s, these two projects continued, but in a united form, as active immunotherapy with viral oncolysates for sarcoma and melanoma (and kidney carcinoma to be added later) (Figures 1A,1B). By then, the Institutional Surveillance Committee required that we inactivate (or ‘‘attenuate’’) the live PR8 influenza virus in our VO preparations. We complied, but by titrations we found some residual low titers of live influenza virus remaining in these lysates (which were used for human immunotherapy) [125]. The live PR8 virus exerted oncolysis in cultured cells of many human tumors, especially sarcomas, melanoma, kidney and ovarian carcinomas; we tested it on a large ‘‘bank’’ of human tumor cell lines established in our laboratory

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Figure 1 1A. The first chemo–immunotherapy protocol designed for the treatment of patients with metastatic sarcomas was approved in 1971–1972 at The University of Texas M. D. Anderson Hospital, Houston, TX. The protocol was designed to determine whether immunotherapy increased sarcoma-specific immune reactions in vitro. These reactions were [1] titrated antibodies for cytolysis with complement and [2] tested in indirect immunofluorescence assays for cell surface, cytoplasmic, or intranuclear bindings with autologous or allogeneic sarcoma cells, and for [3] lymphocytes extracted with ficoll-hypaque from the buffy coats and tested in a chamber-slide cytotoxicity assay against autologous and allogeneic primary and established tumor cell cultures, [4] with or without antibodies added. The project was ‘‘approved but without funding’’ by the National Cancer Institute, National Institutes of Health, Bethesda, MD [109,117–120,130–134,146,147].

Figure 1 1B. Thereafter, immunization with X-irradiated sarcoma cells was omitted and only viral oncolysates (VO) were used for ‘‘active tumor-specific’’ immunizations. The PR8 influenza A virus was used to prepare VO. Over the site of intra- or subcutaneous VO inoculations, live Chicago BCG was scarified. Later, patients with malignant melanomas of adverse prognostic factors (deep or ulcerated primary tumors; satellitosis or in-transit metastases; regional lymph node metastases, visceral metastases with or without surgical removals of gross disease) were included. These protocols were active from 1972 to 1976. These and related protocols were reactivated at the Department of Gynecologic Oncology of the same institution in the early 1980s as ‘‘immunotherapy for gynecological tumors with virus-modified tumor cells’’ [109,118,182–186].

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[126]. Even in vivo, the PR8 virus on occasions performed quite well: We observed regression of directly injected Kaposi’s sarcomas (in the pre-AIDS era). In one case, in a female patient, a hemangiosarcoma of the scalp sloughed off after direct inoculation of the PR8 virus; however it regrew and resisted repeated viral inoculations while the patient developed high titers of antibodies, inhibiting viral hemagglutination and neutralizing the virus. The case of another patient (hospital chart on microfilm), whose biopsy-proven hemangiosarcoma regressed during an influenza-like upper respiratory tract infection, remains an anecdote, inasmuch as laboratory proof for the viral infection has not been provided [127]. However, because influenza viruses readily recombine with each other, there was a possibility that the PR8 virus used might regain its virulence by recombination with one of the newer-generation influenza viruses circulating in the human populations. As a case in point, it was shown that a Russian ‘‘inactivated’’ influenza virus vaccine acquired new virulence through recombination (‘‘multiplicity reactivation’’) in nature, and caused fatal illnesses in Mongolian camels [128]. We reported and published the results of our clinical trials with viral oncolysates at the then famous and wellattended Chicago Symposia (identified in the references). Once published there, the work lost its qualification for publication in journals that insisted on receiving manuscripts not published anywhere else prior to their submission; we conscientiously observed this rule. Therefore our work received no wide recognition: Only investigators who actually worked along the same lines referred to them (very favorably so), and now our work of the 1970s has fallen into oblivion. In recapitulating some of our clinical trials, we treated with VO adult patients with metastatic sarcomas at the Section of Clinical Tumor Virology and Immunology and at the clinical Melanoma-Sarcoma Service, Department of Medicine of The University of Texas M.D. Anderson Hospital in Houston, TX. The chemotherapy regimens in the pre-doxorubicin era consisted of vincristine, cyclophosphamide, actinomycin D and methotrexate (often in high dose with leucovorin rescue); after adriamycin (doxorubicin) became available, it was the


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CyVADIC regimen in which DTIC (dacarbazine) was believed to have acted additively to adriamycin, and chemotherapy courses were administered at 28-day intervals. Of 49 patients treated with chemotherapy only, 36 (72%) progressed over a 6-month observation period eventually to death, occurring within the observation period or later. Of 19 patients receiving CyVADIC chemotherapy with BCG scarifications, 10 (53%) progressed within the same period of time, eventually to death. Of 19 patients treated with CyVADIC chemotherapy and PR8 VO prepared from autologous (preferred) or allogeneic cultured sarcoma cells and administered intra- or subcutaneously with BCG scarified over the inoculation sites of the VO on the fourteenth postchemotherapy day, when the patients’ white blood cell counts were on the rise, 6 (32%) progressed in the same observation period, eventually to death [129,130]. The NCI considered our grant applications of ‘‘low priority; approved without funding,’’ even though we requested support for a prospectively randomized clinical trial with stratification of subgroups of patients. Our clinical trials with melanoma included postoperative patients with deep primary melanomas; patients whose regional lymph node metastases were surgically removed; or patients with gross metastatic disease in various viscera. This was the era when adjuvant chemotherapy and BCG scarifications were extensively tried to suppress micrometastases left behind after surgical removal of primary tumors or tumors metastasizing to regional lymph nodes or to treat gross metastatic disease. Dacarbazine, actinomycin D, and the nitrosourea semustine constituted the chemotherapeutic agents used. Of 27 patients of all stages and with adverse prognosis receiving chemotherapy and BCG, 14 (52%) progressed in a 6-month observation period and eventually died. Of 36 patients of all stages and with adverse prognosis receiving chemotherapy, BCG, and PR8 VO prepared from cultured autologous (preferred) or allogeneic melanoma cells between courses of chemotherapy with BCG scarified over the sites of inoculation of the VO, 14 (39%) progressed and eventually died. Patients with Stage IV disease formed three groups: 19 patients received chemotherapy only with zero complete re-

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missions (CR) and 86% progression rate; 24 patients received chemotherapy and BCG with two CR and a progression rate of 73%; and 11 patients received chemotherapy, BCG, and PR8 VO with one CR and a high progression rate: six of eight adequately treated and three inadequately treated patients progressed. In each of these three groups of very ill patients, there were several who could not tolerate the treatment (especially semustine, which was not licensed) and were ‘‘inadequately’’ treated. However, when survival times were compared, patients with Stage IV disease who received chemotherapy, BCG, and PR8 VO survived a mean of 12.8 months vs. 5.1 months for patients receiving chemotherapy only and 6.25 months for chemotherapy and BCG [131–133]. When these results were reported at the 12th International Cancer Congress in Buenos Aires, Argentina in 1978, the trend favoring patients who also received melanoma VO was ignored; statistically highly significant results of tumor regressions were expected and the consecutively occurring minor responses (rare partial remissions, more frequent stabilization of disease, prolonged survival) were dismissed. Patients with metastatic tumors evaluated today are counted as responding if the disease stabilizes and no progression occurs for several months; these results were below our expectations in the 1970s. Stratification of these patients into comparable subgroups posed close to insurmountable difficulties. The NCI again considered the work ‘‘of low priority; approved without funding’’; the approval was of a small consolation without the funds of the NCI, which then was operating with the increased budget of President Nixon’s ‘‘Conquer of Cancer’’ program. BCG itself and Corynebacteria as immunostimulants for cancer patients were of ‘‘high priority’’ at that time. These simplistic and now abandoned measures received extraordinary NCI support and funding, whereas more sophisticated interventions decades ahead of their time were not understood or supported by that noble institution. These and other patients overlapping with these groups, or independent from these groups, were reported elsewhere, always showing a trend favoring patients who received VO in addition to standard therapy, but not quite reaching an


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overwhelmingly significant advantage at the end of prolonged observation periods [134]. We recently reported the case of a patient exemplifying those who fail despite chemobiotherapy (including interferon-␣2b and interleukin-2 [IL-2]), NDV oncolysate, direct intratumoral injections of NDV, GM-CSF (sargramostim), and immune lymphocyte infusions [135]. Metastatic melanoma remains an incurable disease. Our present NDV oncolysate (autologous VO preferred) protocol for adjuvant therapy aimed at the eradication of melanoma micrometastases is combined with subcutaneous injections of either interferon-␣2b or IL-2. For stage IV disease, we alternate biochemotherapy with immune lymphocytes: lymphokine-activated killer (LAK) cells, a subpopulation of NK cells obtained from the blood or CD4 and CD8 immune lymphocytes extracted from autologous tumors (tumor-infiltrating lymphocytes: TIL), both administered with low-dose (5 million units) subcutaneous IL-2 [136,137]. We can measure quantitatively antibody- and lymphocyte-mediated cytotoxicity aimed at the patient’s tumor cells before and after immunotherapy (but must use the same target cell population for valid evaluation).

IMMUNE REACTIONS Incorporated in our projects of the 1970s were tests for autologous and allogeneic antitumor immune reactions of patients quantitatively evaluated before and after active immunizations with VO. We measured humoral and cell-mediated immune reactions at a time when monoclonal antibodies were yet to be discovered. Our early observation (1969–1970) that antibody-producing lymphoid cells can fuse with lymphoma cells and thereby continue the secretion of a specific antibody was not translated into practical therapeutic use of the antibody produced by the fused (‘‘chimeric’’) cells (Figures 2–4A,4B) [138–142]. At that time, the separation of B, T, and NK lineages and their subgroups of lymphocytes was not yet clearly defined

Figure 2 The first concept of the ‘‘natural hybridoma’’ formation as depicted and presented in 1969 [138]. Expressing budding retrovirus particles, a diploid murine lymphoma cell fuses with an autologous plasma cell secreting retrovirus-neutralizing antibodies. It was clearly recognized what the fused cells were: ‘‘… tetraploid immunoresistant lymphoma cells in the mouse emerge by fusion of the diploid virus-producing lymphoma cell with a plasma-cell producing virus-


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Figure 3 Suspension culture cell line 噛818 consisted of immortalized specific antibody-producing poly- and tetraploid lymphoid cells that grew as highly malignant ascitic tumors in mice (see Fig. 4A,4B). The immune globulins extracted from the culture fluid (by Dr. Roman Pienta) exerted minimal retardation of growth or no effect at all (Dr. Eiichi Shirato) on the pathogenicity of the lymphoma cells (for references, see Chapter 2, ‘‘New Biological Therapeutics,’’ Part IV, Ref. 78–82,84,85 in this volume). (From J Med 1985; 16:509–524.)

䉳 specific globulins… The resulting tetraploid cell will retain malignant growth potential and the genetically determined committedness of both parent cells—to produce leukemia virus, as coded for by the viral genome within the neoplastic cell, and to synthesize virus-specific globulins, as coded for by the genome of the plasmacell’’ [139]. The tetraploid fusion product cells remained alive in culture and in ascites tumors of mice and continued secreting the antibody (under the care of Dr. Jose Trujillo†) [140]. (From the volume Leukemia-Lymphoma, A Collection of Papers Presented at the Fourteenth Annual Clinical Conference on Cancer, 1969, at The University of Texas M. D. Anderson Hospital and Tumor Institute at Houston, Texas. Chicago: Year Book Medical Publishers, Year Book Medical Publishers, 1970.)

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either. We observed and photographed in the early 1970s spectacular encounters between tumor cells and autologous and allogeneic host lymphocytes (Figures 5–8) [143–150]. Large lymphocytes with granular cytoplasm frequently killed allogeneic tumor cells by lysing the cytoplasm of the tumor cells. Blood samples of healthy (tumor-free) individuals (first among them this author) yielded such cells. Smaller lymphocytes with more compact nuclei frequently killed autologous tumor cells by clumping the nuclei of the tumor cells. The phenomenon of apoptosis was not yet recognized as ‘‘programmed cell death,’’ as it is known today. After immunization with VO, the numbers of antitumor cytotoxic lymphocytes increased. Regarding serology, there existed antibodies blocking lymphocyte-mediated cytotoxicity; after immunization with VO, these antibodies were replaced by antibodies that intensified lymphocyte-mediated cytotoxicity [151–154]. Blocking ‘‘serum factors’’ worked against the small lymphocytes in autologous settings; serum factors intensifying cytotoxicity worked best with the large lymphocytes in allogeneic settings. It was not known to us in 1969 and the early 1970s that what we called small lymphocytes were immune T cells. The ‘‘large lymphocytes’’ were designated later to the class of NK cells. With their Fc receptors, NK cells could practice the as yet 䉳 Figure 4 A, 4B Reproducing natural hybridoma formation in 1969 by injecting intraperitoneally antibody-producing normal diploid plasma cells and retrovirus antigen- expressing diploid lymphoma cells and recovering from the peritoneal cavity large poly- and tetraploid fused cells that grew in vitro or in the mouse in vivo in an immortalized fashion and continued the expression of deformed retrovirus particles and the secretion of antibodies specifically neutralizing the retrovirus [138,139]. These experiments were successfully repeated by Dr. H. David Kay (M.D. Anderson Hospital Reseach Report, 1970, pp 331–336; 1972, pp 476–479; 1974, pp 454–455). In 1969–1970, this phenomenon was not referred to as ‘‘natural hybridoma formation’’ (for further references, see Chapter 2, ‘‘New Biological Therapeutics,’’ Part IV, Refs. 78–82,84,85, in this volume). (From J Med 1985; 16:509–524.)

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Figure 5 Relationship of lymphocytes with host stromal cells and with tumor cells. B-CLL cells rest and multiply within large autologous fibroblast-like cells after explantation: the ‘‘feeder layer principle.’’ Otherwise the leukemic cells would die. Both participants of this union survive. On occasions, cytoplasmic bridges connect the lymphocytes with the host cells [148,149] (for further reference, see Chapter 2, ‘‘New Biological Therapeutics,’’ Part I, Ref. 57).

undiscovered ADCC reaction (hence the explanation for ‘‘unblocking serum factors’’ intensifying lymphocyte-mediated cytotoxicity). These were the lymphocytes whose numbers increased first after the administration of VO in tumor-bearing patients. Indeed, one of the physiological functions of the in䉴

Figure 6 Plate reproduced with original legends showing microphotographs from the early 1970s. ‘‘Small compact lymphocytes’’ later recognized to be immune T cells and ‘‘large granular lymphocytes’’ later recognized to be natural killer cells kill autologous and allogeneic tumor cells either by cytoplasmic lysis or by nuclear clumping, much later recognized as ‘‘programmed cell death or apoptosis.’’ (From Acta Microbiologica Hungarica 1991; 38:321–334.)


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Figure 7 A & B Plates reproduced with original legends showing microphotographs from the early 1970s, in which lymphocytes coexist with host fibroblasts; ‘‘small compact lymphocytes’’ surround autologous sarcoma cells and appear as if injecting substances into the cytoplasm of the tumor cells with cytoplasmic lysis ensuing; a large lymphocyte vacuolizes the cytoplasm of an allogeneic sarcoma cell; and large and small lymphocytes destroy tumor cells, causing nuclear clumping, while the lymphocytes preserve their integrity as judged by their intact morphology and tinctorial charactersitics. These lymphocytes remained viable and, when transferred into new tumor cell cultures, they could kill tumor cells again. (From Annales of Clinical and Laboratory Science 1986; 16:488–496).


Figure 7 (Cont)

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nate NK cells is to protect the host against virally infected cells. Immune T cells appeared later, when viral antigens were processed and presented by the as yet undiscovered dendritic cells. These sequences of the immune reaction were not well known in the early 1970s. For metastatic disease, we had to incorporate the active immunization with VO (and live BCG scarified over the site of the intra- or subcutaneous inoculations of the VO) into standard schedules of chemotherapy regimens because it would have been ethically unacceptable to withhold standard therapy in favor of an entirely investigational treatment regimen from these patients (Figures 1A,1B). It was observed in vitro that tumor cells that survived exposure to cytotoxic lymphocytes not only resisted, but actually could kill, the lymphocytes (H. D. Kay and J. G. Sinkovics: Project M30/gm23. Self-defensive Mechanisms of Tumor Cells, 1976).* Only much later could we connect the killing of lymphocytes by tumor cells with the expression of Fas ligand by the tumor cells [155,156] (Figures 8–10A,10B). It was in 1968–1969 that I observed that my own lymphocytes appearing in stained preparations as large cells with granular cytoplasm killed a variety of allogeneic tumor cells; we referred to the phenomenon as ‘‘Burnet’s immune surveillance at work’’ and did not call those lymphocytes ‘‘natural killer cells: NK’’ (H.D. Kay and J.G. Sinkovics: Project M30/ gm21. An Investigation into Antitumor Surveillance of Normal Individuals, 1976)* [138,143,148,157]. Our pioneering (ahead of its time) and impeccably conducted projects had to be abandoned at M. D. Anderson Hospi*

All Projects cited in this chapter are listed in the bi-annual Research Reports of The University of Texas M.D. Anderson Hospital, Printing Division, Austin, TX, 1962–1980.

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Figure 8 Plate reproduced with original legend showing microphotographs from the early 1970s. Some of the lymphocytes attacking tumor cells also die, with nuclear clumping resembling apoptotic death (which was not recognized as such in the early 1970s). (From Acta Microbiologica et Immunologica Hungarica 1997; 44:295–307.)

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Figure 9 Apoptotic deaths commonly occur in large cell diffuse malignant lymphomas. Both large lymphoma cells and small, healthy-appearing host cells die. (From the clinical material of the author, St. Joseph’s Hospital, Tampa, FL.)

tal in the late 1970s because of the ‘‘approved without funding’’ ratings that our grant applications received. Much later, Joseph Horvath and I resumed work along these lines at the Cancer Institute of St. Joseph’s Hospital in affiliation with the University of South Florida College of Medicine in Tampa, FL. In the early 1970s, W. Cassel received approval from Emory University’s Surveillance Committee to use live attenuated NDV (passaged in murine ascites carcinoma). The generous gift of his 73T NDV strain allowed us to switch from PR8 VO to the use of NDV VO (J. C. Horvath, Chapter 5 in this volume). After lymphocyte-mediated killing of human tumor cells was rediscovered at the NCI, where major projects for the therapeutic use of LAK cells and TIL driven by ‘‘T cell growth factor,’’ IL-2, were launched in the mid-1980s, we could incorpo-


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Figure 10 A, 10B Fas-receptor-positive large lymphoma cells (dark red cytoplasm) are attacked by presumably FasLⳭ host lymphocytes (A), while Fas-ligand-expressing lymphoma cells (faint red cytoplasm) escape immune attack by host lymphocytes, whereas some presumably Fas-receptor-expressing lymphocytes appear to die, with nuclear clumping. Histochemical stains with commercial Fas-receptor and Fas-ligand antibodies, horseradish peroxidase technique, and counterstain with H&E (with the help of Professor Bela Bodey, Los Angeles, CA, 2000). (From the clinical material of the author, St. Joseph’s Hospital, Tampa, FL.)

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rate this modality for the treatment of metastatic melanoma and kidney carcinoma in our program [136,137]. MORE RECENT HISTORY In 1962 and thereafter, at the Roswell Park Memorial Institute in Buffalo, NY, veterinary viruses apathogenic in the human host were adapted to tissue cultures of human tumors and then used for the therapy of patients with various cancers [158,159]. Again, remissions so induced were lost to relapses and the project was abandoned. In a personal note, David Yohn explained to this author that fear of possible recombination of the veterinary virus with latent related or unrelated human viruses contributed to the denial of licensure for the clinical use of this procedure. The clinical trials with a veterinary NDV vaccine (renamed MTH-68N virus) conducted (but now discontinued) in Hungary have been referred to extensively elsewhere [61]. In the meantime, in Japan in the 1970s, live attenuated mumps virus was found to induce remissions of human ovarian and other carcinomas and glioblastomas [160–162]. Teruo Asada, in a letter addressed to this author, stated that public health authorities of that country disallowed the use of live mumps virus for cancer therapy; only investigational trials supervised in qualified institutions may be continued. Yoshio Shimizu also abandoned the use of mumps virus for the treatment of ovarian carcinomas [162]; we invited his contribution to this volume but he declined. In 1978, the Hokkaido University published Hiroshi Kobayashi’s monograph on the artificial xenogenization of tumor cells. Tumor cells infected with the Friend erythroleukemia virus of mice suffered no direct oncolytic effect from the virus, but evoked strong antitumor immune reactions from the host [163,164]. Later, in 1989, at a M. D. Anderson Hospital symposium, these authors presented work on tumor cell xenogenization with viral gene transfers (Friend virus env gene; influenza A virus hemagglutinin gene) into tumor cells, rendering the tumor cells more antigenic in their hosts. At the European Association for Cancer Research symposium in Athens, Greece, in 1989, I reviewed this work in comparison with the


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direct effect of oncolytic viruses [165]. Unfortunately, the Moloney mouse leukemia virus envelope protein, when expressed in the membranes of tumor cells, elicited the opposite effect in both allogeneic and syngeneic systems, whereby the tumor cells became immunosuppressive and evaded rejection [166]. Curiously, this article, edited by George Klein, did not mention tumor cell xenogenization by Kobayashi, or the controversy regarding results obtained with the Friend virus previously and differing from those obtained with the Moloney virus, as both retroviral envelope proteins are expressed by tumor cells. The human genome harbors large numbers of nonfunctional retrotransposon-like elements. These include mobile insertional DNA sequences; short and long interspersed elements; ␺g pseudogenes deriving from retrotranscribed mRNA; long terminal repeats and endogenous proviral DNA sequences existing as remnants of prior exogenous retroviral infections poised with the potential to spring into action as new retroviruses or evolve into useful genes. The RAG1, 2 system, telomerase, syncytin in the mammalian placenta, or centromers directing cell divisions and many others take their origin from genomic retrotransposons. Endogenous retroviruses, by gaining env sequences (‘‘natural xenogenization’’) appear as budding particles in syncytiotrophoblasts of the placenta, teratocarcinomas, certain breast cancers, lupus erythematosus and multiple sclerosis, and in lymphoma and leukemia cells, especially when lymphocytes undergo somatic hypermutations of theVDJ sequences initiated by the RAG1, 2 enzymes. Endogenous retroviruses also exist in Kaposi’s sarcoma and other sarcoma cells. A xenografted human tumor may pick up endogenous retroviruses of its new host (Figures 11–13). These env proteins and other retroviral structural proteins may induce autoimmune or antitumor immune reactions, or they may immunologically compromise the host. However, their exact role remains quite underestimated [167*, *

In this article [167], because of regretful mislabeling of two electron microscopic prints, the retroviral particles shown in Figure 12 are now identified to be not in Reed-Sternberg cells, but in Kaposi’s sarcoma cells, as shown in a new reference [171].

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B

Figure 11 Plate showing budding endogenous retrovirus particles in human B lineage lymphoma cells presumably activated by acquiring new env gene-coding sequences during somatic hypermutation [167–170]. Transmission electron microscopy, original magnifications 40,000 and 30,000. (From Orvosi Hetilap [Hungarian Weekly Medical Journal] 2001; 142:1352–1353.)

168–170] and it is entirely unknown how resident cellular retrotransposons react to oncolytic viruses. In the 1980s, W. Cassel’s 73T NDV strain was used again (as a gift of Dr. Cassel to a Chicago team) to kill xenografted human neuroblastoma and fibrosarcoma and various carcinoma cells without harming the tumor-bearing host [172]. This work was editorialized in the Journal of the National 䉴 Figure 12 A, and B Herpesviruses (CMV; HHV-8) and unidentified, presumably endogenous, retroviruses (Fig 12C) share a Kaposi’s sarcoma tumor [167–171]. Transmission electron microscopy, original magnifications 120,000 & 50,000 (†Ferenc & †Phyllis Gyorkey, Joseph Sinkovics, VA Medical Center, Houston, TX, 1983). (A: From J.G. Sinkovics, J.E. Harris, in: J.E. Harris, J.G. Sinkovics, authors. The Immunology of Malignant Disease, second edition. St. Louis: C.V. Mosby, 1976: fig. 5.5, p. 432.)

A

B

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Figure12C

Cancer Institute [173] announcing that a ‘‘new era’’ for the virus therapy of cancer had begun. The origin and relationship of NDV 73T and a new NDV strain—P701—now used for clinical trials by the same investigators [61,174] who revitalized the field of the virus therapy for human cancers in eradicating human tumor xenografts with W. Cassel’s 73T NDV have not been clearly explained, however. What is the origin and derivation of the new P701 NDV? Is it related to 73T NDV or is it entirely different from it and, if so, are the results of the preclinical work done with 73T NDV applicable to P701 NDV? VIRAL ONCOLYSIS TODAY Influenza Virus The negative-sense ssRNA influenza orthomyxovirus, with its 13.6 kb fragmented genome, is re-emerging as an oncolytic


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Figure 13 Murine retrovirus particles picked up by a human tumor xenograft [126]. Transmission electron microscopy, original magnification 35,000 (†Ferenc & †Phyllis Gyorkey, Alex Sandor Gergely, Joseph Sinkovics, VA Medical Center, Houston, TX, 1977).

agent. Its genome is transcribed within the nucleus of the host cell under the direction of its nucleoprotein (NP) [175]. This NP is a multifunctional RNA-binding protein of 498 amino acids with kinase activity. It interacts with the viral RNAdependent RNA polymerase, the viral matrix protein, importins/exportins, export receptor CRM-l, F-actin, and the enzyme helicase. Dendritic cells of the infected host produce interferons, phagocytize apoptotic influenza virus-infected

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cells, and express the viral antigens to CD4 and CD8 T cells, eliciting a Th1 response in which CD8 T cells secrete IFN␥ and inhibit a Th2 response. Interleukin-5 levels drop but eotaxin/CC chemokine ligand 11 and chemokine ligand 2 (monocyte chemoattractant protein-1) levels rise. Influenza virus-infected cells elicit a strong MHC class I-restricted CD8 T cell-mediated immune response [176,177]. The nonstructural viral protein NS1A suppresses the formation of anti-viral mRNAs and inactivates the cellular enzyme PKR, the dimerizing and autophosphorylating serine/threonine protein kinase, which is activated by interferon. The activated (phosphorylated) PKR blocks protein synthesis, including that of viral structural proteins. The PR8 influenza A virus with deleted NS1A gene cannot inactivate PKR; therefore, infected healthy cells allow its replication. However, in cells of STAT knockout mice (no signal transducer and activator transcription), or in tumor cells harboring a mutated ras gene, cellular inhibitors have already incapacitated PKR. In these cells, the PR8/ 34delNS1 virus replicates uninhibited, whereas healthy cells of the same host suppress its replication. Herein lies the selective oncolytic potency of the genetically engineered influenza A virus strain [178,179] (M. Bergmann and T. Muster, Chapter 6 in this volume). Attenuated temperature sensitive (‘‘cold-adapted’’) live influenza viral vaccines are being developed for intranasal instillation and show a reduced ability to recombine [180,181]. Mucosal immunity is primarily mediated by secretory inmmunoglobulin A and, when generated by the vaccine, may prevent the initiation of infection with wild influenza virus. These influenza virus strains may replicate in cancers of the oral or nasal cavities (not yet tested) or possibly produce viral oncolysates safer than those prepared from the PR8 virus in the early 1970s (Figure 14) [129–132]. However, these earlier PR8 influenza A viral oncolysates remained in use for the treatment of gynecological cancers (ovarian adeno- and vulvar squamous cell carcinomas) at M.D. Anderson Hospital in Houston, TX until recently [182–186]. Apparently, after being reclassified as ‘‘virus-modified autologous or homologous extracts’’ and administered to gynecologi-


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Figure 14 Ewing’s sarcoma cell line 噛1846 [126] infected with PR8 influenza A virus in preparation of viral oncolysate (1972). Transmission electron microscopy, original magnification 40,000. (From Intern Rev Immunol 1991; 7:259–287).

cal patients, funding (that was not provided for melanoma and sarcoma patients in the 1970s) became available in the 1980s at the same institution, but at a different department, where the preventive therapeutic and antitumor immune stimulatory value of influenza A viral oncolysates were appreciated [119,184,185]. Any influenza viral strain used for oncolysis must be deprived of its ability to recombine with a wild strain. For example, H1N2 influenza A viruses (Egypt/96/02; Saudi Arabia/ 2231/01) emerging in 2001 were shown to be reassortants between H1N1 (New Caledonia/20/99; Madagascar/55/94/00) and H3N2 (Moscow/10/99; Panama2007/99) viruses [187]. Superficially reviewed (not checking directly for virally induced

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remissions, if any), natural influenza viral infections in patients of a cancer hospital were followed by life-threatening bacterial pneumonias [188,189]. Measles Virus One of the most vicious and notoriously immunosuppressive viruses, the enveloped wild type measles virus (MV), with its 16–20 kb helical RNA genome, is a member of the Paramyxoviridae family within the genus Morbillivirus. Measles remains endemic [190]. The virus attacks dendritic cells and T lymphocytes and induces their apoptotic death, but its attenuated derivative strains replicate in, and kill, human myeloma or glioblastoma cells (S. J. Russell and associates, Chapter 3 in this volume). The Janus protein kinases (JAK) are phosphorylated when the cytoplasmic domains of INF␣␤ type I receptors are phosphorylated, which occurs after the extracellular domain captures its ligand. Activated JAK phosphorylates the signal transducer and activator of transciption (STAT) system, which in turn activates IFN-responsive promoter elements. Members of the Paramyxoviridae inactivate the IFN signaling pathway at many levels. Rubulaviruses (NDV) and mumps virus deplete STAT proteins. MV suppresses JAK phosphorylation and downregulates IL-12 production by monocytes–macrophages. The MV nucleocapsid protein binds to Fc␥RIII and inhibits the generation of humoral immunity. When the virus infects dendritic cells (DC) and epidermal Langerhans cells, inducing cell fusion and abrogating DC and CD4 T cell interactions, ultimately both DC and T cells die apoptotic deaths [191–198]. In a Chinese clinical trial [199], when its immunosuppressive effects might have been counterbalanced with the coadministration of BCG (an extremely precarious balance it must have been!), MV added to chemotherapy for acute leukemias induced the highest remission rates. Remissions were in the 80% range in the MV-treated group of patients vs. only 31% remission rates in chemotherapy-only control patients; remission rose to 45% when only BCG was added to chemotherapy. Standard MV strains (Edmonston; Halle) enter cells through


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the CD46 receptor. Another MV receptor, the signaling lymphocyte activation molecule (SLAM; CD150) is expressed on lymphocytes, including memory cells, CD4 cells, Th1 cells, and EBV-transformed B cells [200]. This latter event may explain the regressions of African Burkitt’s lymphoma or Hodgkin’s disease in children experiencing natural infection with MV [52]. The former event (loss of memory T cells) explains death caused by natural measles infection in patients with nonHodgkin’s lymphoma [201]. Measles virus and antibodies may form large amounts of immune complexes (‘‘atypical measles’’) [202] and MV may cause acute sclerosing panencephalitis. Hamster brain tumor cells persistently infected with MV and exposed to antiviral antibodies gained an enhanced growth rate [203]. Attenuation of the wild Edmonston MV [204] was achieved by passages of the virus through human kidney and amnion cell cultures (Edmonston-Enders strain) and through chicken embryo amnion and fibroblast cells (Moraten vaccine strain). The Zagreb strain was passaged in Wistar Institute human diploid fibroblast cultures (WI-38). To direct the attenuated vaccine strain of MV exclusively into myeloma cells, the virus particle must express a single-chain antibody directed against the myeloma cell receptor CD38. When used against ovarian carcinoma or glioblastoma cells, the Edmonston attenuated MV enters through the CD46 receptor, which is overexpressed in the tumor cells (Russell and Associates, in this volume). In orthotopically transplanted human glioblastoma xenografts, the genetically engineered Edmonston vaccine measles virus (MV-CEA) revealed its presence by releasing CEA from the infected tumor cells before complete destruction of the tumors occurred, leaving glial scars and some inflammatory cells behind. The Edmonston MV-CEA completely destroyed xenografts of the CD46Ⳮ SKOV3ip.1 human ovarian carcinoma cell line in athymic mice [205–208]. Thus, MV closes ranks with NDV and vesicular stomatitis virus (VSV), considered to be ‘‘naturally oncolytic viruses.’’ Rubella virus also can attack selectively astrocytes but its apoptosis-inducing activities were studied in Vero cells possessing intact wild p53 [209–211]. Possibly, the attenuated

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live rubella virus (Meruvax, Wistar Institute RA 27/3 strain) would attack human tumor cells with deleted (neutralized by MDM2 protein) or mutated p53. Also, this virus, when combined with the Jeryl Lynn strain of attenuated mumps virus (Biavax, Merck & Co., Whitehouse Station, NJ) might exhibit a increased (or lost) oncolytic potency (if any). Newcastle Disease Virus The enveloped, negative-stranded helical RNA NDV belongs in the genus Rubulavirus within the family of Paramyxoviridae. NDV is the causative agent of fowl plague, a highly contagious disease of poultry. Virulent strains could be recovered from its cloned cDNA [212] (J. C. Horvath, Chapter 5 in this volume). NDV can cause conjunctivitis, with enlargement of the preauricular lymph node, in human beings (‘‘the oculoglandular syndrome’’ described by M. Radno´t in Hungary, who initiated in 1948 our studies of virus isolation from human conjunctival washings) [213,214]. Rubulaviruses evade the host cells’ interferon response by V protein production that targets STATs (see New Biological Therapeutics by Sinkovics) for proteasome-mediated degradation [215] and thereforce can replicate their progeny to full maturation, resulting in cell death. When the host cell dies from apoptosis early during the viral cycle, however, no infectious viral particles are formed and there is no further spread of infectious virus within the tumor mass. Even when the viral replication cycle is incomplete in a given tumor, such as with the Ulster strain of NDV (V. Schirrmacher, Chapter 9 in this volume), host antibodies, activated macrophages, antigenloaded dendritic cells, NK cells, immune T cells, and lymphoand cytokines produced by them mediate destruction of the infected cell [216–221]. It is debated whether fully replicative, early apoptosis-inducing, or incompletely replicating but cytokine- and immune reactions-evoking NDV strains exert the best oncolytic effect. If a transfected NDV gene encodes viral hemagglutinin-neuramidase antigenic proteins in a tumor cell (like in a murine myeloma cell), the host’s tolerance will be overcome and host-vs-tumor immune responses will be evoked


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[222,223]. Could virus-neutralizing antibodies curtail cell-tocell viral spread in a tumor mass? Indeed, the possession of hydrophobic fusion peptides within the viral envelope promote syncytium formation of infected tumor cells, whereby the virus spreads without an extracellular phase and renders the syncytiosome highly immunogenic (as in the case of vesicular stomatitis virus, vide infra). The early apoptotic death of NDV-infected rat pheochromocytoma cells [224,225] is probably not a valid model of NDV oncolysis for the tumor-bearing human host. Despite of the high publicity it receives [59–61,226], the claim of the sponsor of this report, that 20 CR and 9 PR in 29 patients with ‘‘advanced cancers’’ occurred in response to NDV (MTH-68/H) treatment [224], should be viewed with great reservations (unless confirmed convincingly and independently) [156]. W. Cassel, in the early 1960s, induced the death of human adenocarcinoma cells implanted in hamster cheek pouches by direct intratumoral injections of NDV [10]. The same virus induced temporary regression of uterine cancer in a patient [10]. W. Cassel was first to declare NDV to be an antineoplastic agent [10] and translated the outcome of animal experiments into a successful clinical therapeutic trial (W. Cassel, Chapter 9 in this volume). It is not yet proven whether oncolytic viruses that perform so well against cultured or xenografted human tumors, such as W. Cassel’s 73-T NDV [172], will be able to sustain this level of antitumor activity in the tumor-bearing human host. Whether NDV oncolysates would perform better than direct viral inoculations is unknown because no comparative clinical trial exists. However, W. Cassel’s and V. Schirrmacher’s trials, taken together [122,227–230], indicate that NDV oncolysates as ‘‘preventive vaccines’’ perform very well against micrometastases left behind after surgical removal of gross tumors (melanoma and various adenocarcinomas). A NDV melanoma oncolysate prepared at M.D. Anderson Hospital but using techniques different from those of W. Cassel, induced melanoma cell-specific antibodies in patients, but provided no significant protection against relapses; W. Cassel clarified the issue [231–233]. Newcastle disease virus oncolysates may not

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work as therapeutic vaccines against gross metastatic disease. If it were possible to incorporate NDV in a dendritic cell vaccine [125,234] to be co-administered with IFNs, IL-2, or IL12, its performance might rise to the level of a therapeutic vaccine (V. Schirrmacher; J. C. Horvath; Chapter 4 and 5, respectively, in this volume). In a recent professionally conducted clinical trial [174], using the newly introduced attenuated PV701 NDV strain (without publishing its preclinical performance against xenografted human tumors), some 80 patients with advanced cancers were treated. A few partial remissions (PR), minor responses and stabilizations of disease were recorded but the single complete remission (CR) was lost to relapse. A second Phase I trial using ‘‘desensitization’’ and a very high dose of PV701 NDV (24–120 billion PFU/m2) and prolonged infusion time produced three partial remissions (PR), two minor responses (MR) and four stabilizations of disease in 11 patients with metastatic cancers refractory to standard therapy [235]. Still, no CR could be observed, in contrast to complete eradication by the 73T NDV in preclinical experiments with human tumor xenografts in mice. In a Chinese clinical trial [236] for the treatment of cancers of the digestive tract, 257 patients were treated only surgically; 310 patients received an autologous tumor vaccine and NDV (LaSota strain) therapy in addition to surgical resection. Overall survival was more than 7 years in the immunized group vs. 4.46 years in the surgically treated group. The mean survival time was 5.13 years for the immunized group and 4.15 years for the surgically treated group. A stratification of these patients will be necessary for valid evaluation of these results. V. Schirrmacher (Chapter 4 in this volume) has used the incompletely replicating but cytokine- and immune- reactions–evoking Ulster strain of NDV for human tumor immunotherapy. Dendritic cells pulsed with Ulster NDV oncolysates induce Matzinger’s danger signals, re-enlist memory cells resting in the bone marrow, and react to tumor (breast cancer) antigens. Another German group used the Ulster strain of NDV to prepare glioblastoma vaccines for active tumor-spe-


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cific immunotherapy given postresection and postradiotherapy [237]. Median patient survival was 46 weeks; mean, 60 weeks, ranging from 31 to 105 weeks; only one patient survived (more than 88 weeks), even though the patients appeared to be immunocompetent to the extent that they produced skin reactions to the autologous vaccine inoculations. Relapsing and re-resected tumors were infiltrated by CD4/ CD8 lymphocytes. NDV oncolysates are in use as preventive vaccines administered after tumor removal (melanoma; kidney carcinoma) when clinical criteria are such that persistence of micrometastases is expected (Horvath, in this volume). However, in Germany, kidney carcinoma cells infected with NDV 73T and irradiated with 100 Gy thereafter induced no antitumor antibodies or immune T cells against tumor cells not virally infected. Anti-NDV antibodies exerted ADCC reaction against virally infected tumor cells only [238,239]. Cassel’s 73-T NDV strain was investigated by the U.S. Department of Agriculture in 2003. It was declared to be not a viscerotropic virus. In the laboratory, it may kill newly hatched chickens after cerebral inoculation, but it is not considered to be pathogenic to birds or to human beings through any natural routes of infection. It is safe to use it as live virus in VO preparations. Vesicular Stomatitis Virus The enveloped negative-stranded helical Rhabdoviridae RNA virus with a 13–16 kb genome is oncolytic [240] (R. A. C. Taylor, J. M. Paterson, and J. C. Bell, Chapter 7 in this volume). Vesicular stomatitis virus was shown already in the mid-1960s to kill mouse tumors [241] and have an unusual relationship with IFN [242]. In Finland, it was used for viral oncolysate production to treat mouse tumors in 1971 [243]. In the 1970s, VSV was found to inhibit the growth of, or render murine mastocytoma and L1210 murine leukemia cells more immunogenic in their hosts [244,245]. It is conceivable that Rhabdoviridae and Paramyxoviridae descend from an ancient common ancestor that has con-

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ferred natural oncolytic properties to some members of these families and that these viruses exercise natural oncolysis since their remote past. When VSV was passaged for short, intermediate, or late intervals, viral populations passaged for intermediate intervals were the most stable [246]. It recently was discovered that VSV induces apoptosis in p53-defective human tumor cell lines in vitro or in their xenografts in vivo (G.N. Barber and associates). However, VSV is known to induce apoptosis very early after its entry into the cytoplasm. This effect is not inhibited by cycloheximid. Ultraviolet-irradiated virus particles also elicit apoptosis. The matrix (M) protein of VSV in itself elicits the apoptotic response of the cell and suppresses host cell gene expressions, such as JAK/STAT and IL-6. Tumor cells (HeLa) overexpressing Bcl-2, resist Minduced cell-rounding and apoptosis [247–249]. The VSV fusogenic membrane glycoprotein (G protein) induces multinucleated syncytia of infected human tumor fibro- and osteosarcoma, melanoma, and colon and lung cancer) cells, resulting in cell death caused by premature chromosome condensation and adenosine triphosphate depletion. Dying syncytiosomes load dendritic cells with their surface antigens. A plasmid expression system encoding VSV G protein induced murine colon and kidney carcinoma cells to form syncytia that were highly immunogenic, especially in the presence of IL12 [250–253]. Although VSV-induced syncytia were described much earlier [242], it was recently shown that these syncytia are highly immunogenic and attract NK cells, macrophages, and dendritic cells. Vesicular stomatitis virus antigen processing and presentation occur via MHC class I and class II pathways [254]. In early clinical trials, a VSV human melanoma oncolysate failed to induce the production of melanoma cell-specific antibodies in patients [255]. Tumors with deleted p53, mutated ras or c-myc and glioblastoma cells are susceptible to VSV oncolysis in vitro or as xenografts [256,257]. Human hepatocellular carcinoma cells orthotopically xenografted into immunocompetent rats completely regressed after one intratumoral injection of VSV, although the virus was not able to replicate in healthy hepatocytes. It was not explicitly stated


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whether the virus destroyed the tumor cells or virally infected tumor cells were immunologically attacked by the host, or if tumor cell syncytia were formed. Tumor cell death was described as ‘‘large necrotic areas within the tumor’’ but not in normal liver parenchyma [258]. Vesicular stomatitis virus vectors carrying the herpes viral gene for thymidine kinase (TK) or the gene for IL-4 gain oncolytic potency and evoke granulocytic and T cell infiltrations into the murine tumors against which they were tested [259]. Moloney murine leukemia retroviral vectors pseudotyped for VSV G protein expression and armed with an insulin-like growth factor receptor antisense sequence or with the herpes viral TK sequence inhibited tumor (colon and pancreatic carcinomas) growth and metastasis formation in xenografts. In these xenografts, ganciclovir exerted enhanced bystander effect [260,261]. Indomethacin suppresses the replication of VSV [262], so this medication should be withheld from patients entering clinical trials to receive oncolytic VSV. Reovirus The respiratory–enteric orphan (Sabin) icosahedral naked reoviruses with a 22–27 kb RNA genome cannot readily infect healthy cells because of the cells’ vigorous IFN response, whereas tumor cells with defective machinery for IFN production (especially in ras-mutated tumor cells) are exquisitely susceptible to this virus and die apoptotic death upon viral entry [263]. However, tumor cells inherently resist programmed cell death caused by tumor suppressor gene mutations or deletions. Instead, tumor cells may allow the virus to complete its full replicative cycle, leading to cell death by burst as the new viral progeny exits. Reovirus-induced apoptotic cell death involves either or both the extrinsic (through cell surface death receptors) and intrinsic (through cytochrome C release from mitochondria) pathways [264]. From modest beginnings—that is, immunologically mediated rejection of murine leukemia–lymphoma cells and tumors by reovirus, as reported in 1976 and 1988 (especially in combination with the nitrosourea BCNU)

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[265–267]—reoviruses have now advanced to occupy a prominent place among the most respected oncolytic viruses ready for Phase I and II clinical trials. The reoviral gene S1 is bicistronic and, as such, encodes the viral protein ␴1 that attaches to sialic acid receptors and the nonvirion-associated protein ␴1s that induces cell cycle arrest at G2-M [268]. Some reoviruses may expropriate the EGF-R as their entry site into the cytosol [269]. The reoviral gene M2 encodes the outer capsid protein (␮1c) of the virus particle, which enables the virus to transgress the cell membrane. Proteins encoded by reoviral genes were characterized with the use of monoclonal antibodies from cloned hybridomas [270]. When the nonenveloped dsRNA reovirus (type 3 Abney T3A or Dearing T3D strains) induces apoptosis, both the extrinsic (through cell surface receptor activation involving the tumor necrosis factor or TNF-related apoptosis-inducing ligand released from infected cells) and intrinsic (through cytochrome C release from mitochondria and caspase 7 and 8 activation) pathways are activated [264]. Activation of c-jun–encoded c-Jun kinase occurs in type 3 but not in type 1 (Lang T1L) reovirus infections. The c-Jun proteins either homodimerize or heterodimerize with c-Fos protein and activate nuclear transcription factor AP1 (or the c-jun gene actually encodes AP1). Counterparts of the genes c-jun (1p31–33) and c-fos (14q24.3–22) were discovered as vjun and v-fos in acutely transforming retroviruses (avian sarcoma virus 17 and murine osteosarcoma virus FBJ-MuSV, respectively) and are considered to be proto-oncogenes when activated in adult life. In normal fetal life, however, c-fos and cfms are strongly expressed in trophoblasts. The c-Jun protein also activates NF␬B—an anti-apoptotic event; further, it is essential for the innate IFN␣ and IFN␤ responses [271,272]. However, reoviruses are not oncogenic; they induce or allow pre-existing cell survival mechanisms (as in cells already transformed, especially by ras oncogenes) to function and cause lytic death of cells through full maturation of their progeny, at which time the infected cell dies by burst. Normal cells produce IFN␣ and IFN␤ and disallow full maturation of the viral progeny.


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Although healthy cells are not readily susceptible to reoviral infection, ras-mutated transformed cells are fully susceptible, presenting an environment in which the dsRNA-activated PKR is inactive. This IFN-activated enzyme shuts down protein synthesis in normal cells, including the synthesis of structural proteins of a viral usurper [273]. Without functional (dephosphorylated) PKR, ras-mutated cells succumb to full replicative cycles of reoviruses. Reovirus serotype 3 (Dearing) produced extensive oncolysis of human cancer cells in vitro (in tissue cultures) and in vivo (in xenografts). The most sensitive human tumors were glioblastoma, breast, ovarian, colon and pancreatic carcinomas, and malignant lymphomas [274–278]. In a bilateral xenograft model, whereby the pancreatic cancer cell xenograft was injected in one side, the uninfected xenograft on the other side also picked up and replicated the virus and attracted an NK cell-mediated host reaction [279]. Orthotopically transplanted human brain tumor xenografts (glioblastoma; medulloblastoma) injected intratumorally with reovirus either regressed or showed extremely retarded growth rates and failed to metastasize [280]. In co-cultured spheroids of human transitional carcinoma cells of the urinary bladder and their fibroblasts, reovirus destroyed the cancer cells and selectively spared the fibroblasts [281]. A substantial segment of the human populations have antibodies against reoviruses. It is not known whether the virus will perform as well in clinical trials as it does in its pre-clinical assays or whether pre-existing or newly acquired antiviral immune reactions (antibodies; NK and immune T cells) would counteract or promote viral oncolysis. Vaccinia Virus Vaccinia and ectromelia viruses already excelled in the 1920s as oncolytic agents against murine malignant tumors [94,281]. The large, enveloped vaccinia virus (VV), with its linear DNA genome of over 220 kb, undergoes the following serial stages of maturation within the cytoplasm of its host cell: intracellular mature virus (IMV), intracellular enveloped virus (IEV), cell-

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associated enveloped virus (CEV), and release of extracellular enveloped virus. Vacinia virus replicates exclusively in the cytoplasm. Viral genes B5R and F13L provide packaging for IMV to become IEV. Gene A36R forms the actin tail. Gene A56R forms the hemagglutinin; A56Rⳮ particles produce syncytial plaques in monolayers. Gene F12L product protein transports the virus particle through microtubules to the cell surface. Genes A33R and A34R render the virus particle infectious. The viral gene B8R encodes a 43kDa glycoprotein, which is secreted from infected cells and displays homology for amino acid sequence in a manner similar to the extracellular domain of the INF␥-receptor. It binds INF␥ and neutralizes it, thus depriving the host of its molecular mediator that would have initiated Th1-type immune reactions. The C12L viral gene product protein binds IL-18, which would have otherwise interacted with IL-12 to further initiate Th1-type immune reactions. Viral gene N1L encodes the 14kDa virulence factor. Virus particles lacking N1L genes are fully attenuated. Viral genes B13R and B22R encode serpins that inhibit the IL1␤–converting enzyme and prevent the cell from committing TNF- or Fas-induced programmed death. Viral genes E3L and K3L encode proteins that suppress IFN-induced antiviral cellular proteins. Otherwise, the antiviral state of the cell is set by the IFN-induced serin-threonine kinase PKR and the 2′–5′ oligoadenylate synthetase. Viral gene A41L encodes a chemokine-binding protein. Early gene expression of VV induces apoptotic death of macrophages and dendritic cells by suppressing the anti-apoptotic protein BclXL. Interferon-␥ does not, but Bcl-2 can protect against VV-induced apoptosis. The serine protease inhibitor serpin crmA is a prominent NF␬Bactivator and anti-apoptotic protein produced by poxviruses [282–288]. Monoclonal antibody C3, aimed at the 14kDa trimeric VV membrane protein, neutralizes the virus as it emerges from the cytoplasm of its host cell [289]. Vaccinia virus and other pox viruses nonpathogenic in the human host are being considered for gene delivery systems for gene therapy of human cancers [290–294]. Vaccinia virus elicits strong oncolytic activity or augments in syngeneic hosts the immunogenicity of tumor cells


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expressing both tumor-associated transplantation antigens and VV antigens [281]. Replication-selective oncolytic VV strains are deprived of their thymidine kinase and vaccinia growth factor genes [294]. Genetically engineered VV contain IL-4 and IL-10 genes dictating that the host develop not Th1but Th2-type immune reaction with much delayed viral clearance [295]. The GM-CSF gene-containing VV induced remissions of melanoma skin nodules after direct intratumoral injections [296]. The TA-HPV recombinant VV contains the E6 and E7 genes of HPV-18 and immunizes (mice) against HPV infection [297]. The gene of the overexpressed tumor-associated antigen 5T4 could be inserted into the genome of the attenuated Ankara strain of VV. Mice immunized with this virus rejected murine and human tumor xenografts [298]. When tested in Australia, the Wistar Institute VV melanoma oncolysate showed only a favorable trend in prolonging survival of patients, but without significance (P. Hersey, in this volume). Overall survival was 151 months in treated patients and 88 months in the control patient group. The 5- and 10-year survival rates for treated and control patients were 60% and 53% vs. 55% and 41%, respectively. Median relapsefree survival was 83 months in treated and 43 months in control patients. By the fifth year, these figures fell to 51% for the treated and 47% for the control group [299–301]. Herpes Viruses The icosahedral, enveloped, linear dsDNA-containing herpes viruses with a genome size of 150–200 kb are widely distributed in nature exhibit both oncogenic (EBV and HHV-8) [73–76,302–305] and oncolytic [306] potentials, and evade defensive reactions of their hosts at many levels. Two strains of herpes viruses, rendered avirulent through genetic exchange and fusion, may create virulent recombinants [307]. The coevolution and coexistence of herpes and retro(lenti)viruses of African origin are most remarkable and the presence of both retroproviral DNA sequences, in addition to HHV-8, in Kaposi’s sarcoma cells has been postulated [308] (Figures 12A,12B,12C).

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Herpes viruses can persist in a latent form. Herpes viruses abrogate or evade immune reactions of the host at many levels. Virally encoded complement and Fc decoy receptors, downregulated major histocompatibility complex (MHC) class I and II antigens, and cell surface adhesion molecules (ICAM1 and LFA-3) appear, and suppressed viral antigen processing and presentation to immune T cells are readily practiced by herpes virions. Infected cell protein ICP47 disrupts normal peptide loading on MHC class I molecules, thus averting attacks by cytotoxic T cells. The synthesis of MHC class II molecules is suppressed by viral gene product proteins Vhs and ICP34.5 from genes UL41 and ␥134.5. Herpes viruses express glycoproteins having homology to host cell glycoproteins, including those that imitate G protein-coupled receptors. There is a virally encoded tolerogen and immunosuppressive cytokine—IL-10. The UL40 gene in cytomegalovirus (CMV) codes for a glycoprotein that imitates the structure of the cell surface antigen human leukocyte antigen (HLA)-E, allowing the virus to incapacitate NK cell receptors CD94/NKG2A and thereby avert NK cell attack on virally infected cells. Cytomegalovirus also downregulates epidermal growth factor (EGF) receptor expression and signal conduction (autophosphorylation) of the tyrosine kinase, possibly a pro-apoptotic event. Herpes simplex virus types 1 and 2 block apoptotic response of infected cells, even under conditions of experimental induction by TNF␣, anti-Fas antibody, C2-ceramide or thermal shock. Herpes simplex virus constructs with deleted genes ␣4 and Us3 do not protect infected cells against apoptosis. Apoptosis triggered by the ␣4-defective herpes virus can be blocked by Bcl-2. The virally encoded protein Us3 neutralizes the proapoptotic Bcl-2-associated cellular protein BAD by forming a complex with it, thus preventing programmed cell death. The ICP27 and ICP4 viral proteins of the wild-type HSV-1 are necessary to maintain intracellular levels of bcl-2 mRNA and protein. In an attempt to block apoptosis, deletion mutants ICP27ⳮ and ICP4ⳮ HSV-1 viruses fail to counteract the host cell’s apoptotic response to viral entry.


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Human herpes virus-6, the causative agent of roseola infantum and exanthema subitum, encodes counterfeit and secreted (solubilized) receptors for chemokines RANTES (regulated activation normal T cell-expressed and secreted) and eotaxin-␤. In this case, the infected cell will not bind chemokines and will not attract immune T cells, NK cells, or macrophages. The viral lat gene codes for the anti-apoptotic Lat protein, permitting survival of the infected cell until completion of the viral replicative circle and full maturation of the new viral progeny [309–323]. In mice, HSV-2 acts as a double agent. Replicative viral infection exerts an oncolytic effect on cellular transplants of a syngeneic tumor, whereas enhanced tumor growth occurs in mice harboring latent, nonreplicating HSV-2 infection [324]. Of the 152 kb herpes virus genome that codes for some 89 proteins, 30 kb is replaceable (dispensible for viral replication). Thymidine kinase-defective HSV dlsptk replicates well in rapidly growing glioma cells that abundantly express cellular tk gene, whereas resting brain cells resist the virus, although the virus retains its neurotoxicity and acyclovir fails to inhibit its replication. By deleting the ␥134,5 viral gene, HSV neurovirulence decreases, but the virus retains its selectivity to replicate in malignantly transformed nerve cells. On the other hand, glioma cells (and many other cancer cells) transduced with HSV tk gene by retroviral vectors may be killed by acyclovir-ganciclovir, ionizing radiation, or bromovinyldeoxyuridine [325–335]. In addition to directly attacked tumor cells, ‘‘bystander tumor cells’’ may also succumb [336–338]. This system worked well against HSV tk genetransduced lung metastases of murine melanoma, or glioma grafts, or Lewis lung carcinoma in rats [339–341]. The G207 mutant of the parent HSV R3616 (MediGene, Inc., San Diego, CA) is defective for the ␥134.5 (neurovirulence) genes and contains an inactivated viral ribonucleotide reductase (ICP6) subunit. The cellular counterpart of this enzyme is overexpressed in rapidly replicating tumor cells, where G207 replicates with preference over resting cells and elicits immune T cell reactions of the murine host to infected tumor cells. When the cellular enzyme is inhibited with hy-

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droxyurea, the virus loses its oncolytic potential and ionizing radiation fails to enhance it. Ionizing radiation or cisplatin promote viral oncolysis in xenografts of human uterine cervical carcinomas [342,343]. The G207 mutant virus cannot replicate in the brain of owl (Aotus) monkeys, which are highly susceptible to wild type HSV. G207 is in clinical trials for human malignant gliomas with or without adjuvant radiotherapy and for colorectal, breast, ovarian, and prostate cancers. In a group of patients with high-grade gliomas who were treated intratumorally, two survived 4 years and by autopsy a patient who died of cerebral infarction showed no residual glioma. The virus did not cause encephalitis in any of the patients (additional literature cited: [331–335,344–346]). Cytomegalovirus replicates in human rhabdomyosarcoma cells. Both in Europe and in San Diego, CA, G207 also destroyed childhood rhabdomyosarcoma xenografts [347–349] (but when we applied for its use in one patient, our request was not granted). The fusogenic G207, Fu-10, spreads through syncytia formed by coalescing tumor cells and escapes antiviral antibodies, while showing an increased oncolytic potency [350]. The Synco-2D herpes virus is doubly fusogenic in that it encodes and produces the hyperfusogenic glycoprotein of the gibbon ape leukemia virus, enabling it to eradicate human ovarian carcinoma xenografts in athymic nu/nu mice [351] (Fu, in this volume). The NV1020 HSV construct (R7020, MediGene, Inc., San Diego, CA) with major (700 bp) genomic deletions lacks its endogenous tk gene, one copy of its two ␥134.5 genes and the joint region of the long and short components of its genome, while retaining its ICP6 region. An exogenous copy of viral tk gene was inserted under the control the viral ␣4 gene acting as a promoter. So constructed, NV1020 destroys xenografted human gastric, pancreatic, prostatic, and squamous cell carcinomas and synergizes with ionizing radiation. In investigational protocols, the engineered virus is being injected intraarterially into liver metastases of colorectal carcinomas. The ICP4 gene of HSV mutant G92a is under the transcriptional control of the albumin gene. This gene is overexpressed in hepatoma cells, where G29a replicates to 104-fold


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higher titers than in healthy hepatocytes [331–335]. Cyclophosphamide (CTX) synergizes with oncolytic HSV in more than one way. Herpes simplex virus particles containing the cytochrome p450 oxidase gene activate intracellular CTX for antitumor effects, and CTX exerts an immunosuppressive effect on the host, resulting in suppressed innate immune reactions and low virus-neutralizing antibody titers, allowing for cell-to-cell spread of the oncolytic virus. Complement deprivation achieves similar effects [352,353]. HSV1716 with deleted ICP34.5 protein selectively grows in rapidly dividing tumor cells (melanoma) [354]. Upon direct injection into high-grade gliomas, this deletion mutant induced tumor regressions with greater than 3-year survivals of three of nine patients so treated (at the University of Glasgow, UK) [355,356]. When the two replication-competent multimutants G207 and NV1020 herpes viruses were compared in intraperitoneally growing human gastric cancer xenografts, NV1020 performed better. Against prostatic adenocarcinoma xenografts, both G207 and NV1020 performed equally well [346]. NV1020 kills human head and neck squamous carcinoma cell lines in vitro and the xenografts of these tumors in vivo [357]. Herpes viruses enlisted for gene therapy of human cancers deliver genes into tumor cells—CEA, GM-CSF, IL-2, and the cyclophosphamide-activator transgene CYP2B1. Incorporated are in amplicon plasmids, endostatin or secondary lymphoid tissue chemokine, and CD ligand for the generation of augmented Th1-type antitumor immunity [358–364]. In Hungary, a ribonucleotide reductase null mutant of the pseudorabies (Aujeszky) virus replicated in, and destroyed, human neuroblastoma, glioblastoma, and hepatoma cells and it is considered to be a gene delivery vector for the gene therapy of human cancers [365]. Replication-competent herpes viruses are oncolytic and spread within the tumor. For gene therapy, replication-defective mutant herpes viruses are used as delivery vectors. Adenoviruses The naked icosahedral adenoviruses possess linear dsDNA of 38 kb and are capable of killing cells by lysis, or malignantly

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transforming them, although adenoviruses are not known to cause human cancers. Early after viral entry through the coxsackie-adenovirus receptor (CAR) capturing the fiber knob of, and internalizing, the adenovirus type 5 particle, apoptotic cell death is triggered by viral protein E1A. However, the virus has evolved anti-apoptotic and anti-IFN strategies to spare the host cell until the new mature viral progeny exits. In human cancer cells of the urinary bladder [366], CAR functions as an intercellular adhesion molecule and elicits a growth inhibitory cascade. Tumor cells with low CAR expression grew faster than tumor cells with high CAR expression. Low-grade prostatic carcinoma cells underexpress CAR, whereas its metastasizing cells display strong CAR expression [367]. Like cadherins, CAR may be tumor suppressing in the organ of origin for the tumor, but tumor promoting in an environment distant from the organ in which the tumor originated. In astrocytomas [368], high-grade tumors expressed less CAR than low-grade tumors. In addition to CAR, adenovirus particles also attach to MHC class II molecules and ␣-integrins (the penton base of Ad2). Although human prostate cancer cells express CAR, CAR may not be overexpressed in many other human cancer cells. Solubilized sCAR may inhibit adenovirus particles extracellularly [369]. Adenovirus 5 carrying a gene of adenovirus 3 attaches to a receptor different from CAR and can enter human ovarian carcinoma cells with downregulated CAR expression [370]. As a conditionally replicating adenovirus, AdsCAR-EGF enters human tumor cells through the overexpressed EGF-R [371]. Adenovirus armed with the sCARfC6.5 protein enters cancer cells through the erb2 (HER2/neu) receptor [372]. Coxsackie-adenovirus receptor -independent cellular entry mechanisms through the ␣-integrins facilitate the infection of human kidney carcinoma cells with retargeted adenoviruses [373]. Fibroblast growth factor (FGF)-Ad containing the HSVtk gene targets the basic FGF receptor (bFGF-R) [374], which is overexpressed in proliferating endothelial cells in tumor-induced neoangiogenesis and in certain tumor cells. Adenovirus constructs with an integrin-binding motif (RGD peptide in the fiber knob) enter low CAR-expressor squamous


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carcinoma cells of the oral cavity [333,361,375–380]. Retention of the E3 region in Ad5-⌬24RGD increased its oncogenic potency [381]. Adenoviral replication-defective (E1ⳮ and E3ⳮ) vectors induce immune reactions. For example, the proinflammatory intercellular adhesion molecule ICAM-1 is overexpressed in the infected tissues through activation of mitogen-activated protein kinases (MAP kinases) and (nuclear factor kappa B) NF␬B [382]. The Hungarian adenovirus research team has proposed that viral capsid alterations reduce the antigenicity of the virus, thereby delaying the elimination of adenoviral vectors by immune reactions through virus-neutralizing antibodies of the host [383]. Immunostimulatory adenoviral vectors have also been constructed [384]. The E1ⳮ/E3ⳮ Ad4-1BBL construct carrying the gene for the TNF family ligand 4-1BBL, infects human adenocarcinoma cells, which attract T-LAK cells that are highly cytotoxic for the tumor cells and eradicate tumor xenografts. In addition to NK cells [385,386], immune T cells cytotoxic for adenovirus-infected cells are also mobilized [387,388]. The relationship of adenovirus-infected tumor cells and macrophages is very complicated. Adenoviruses induce dendritic cell maturation [389,390] whereas viral E1A protein sensitizes tumor cells to apoptosis by TNF␣ of macrophage origin. However, E1A also activates heat shock proteins that antagonize TNF␣-mediated apoptosis [391,392]. It is possible to generate cytotoxic T cells reacting specifically with E1A proteins, therefore attacking and destroying adenovirally induced tumors [387]. The adenovirus IFN␥ gene construct TG1041 is expected to upregulate MHC class I and II expression in melanoma cells, rendering the infected cells more immunogenic [393]. E1A proteins also block IFN-induced gene expressions [394]. Although IFNs promote NK cell-mediated lysis of adenovirus-infected cells, they protect noninfected cells from NK cell-mediated cytotoxicity. This is the phenomenon of IFN-mediated resistance to cytolysis or cytoprotection (IFN-MCP). E1A (expression of its first exon) counteract IFN-MCP [386]. Soon after viral entry, the tumor suppressor gene for the Rb protein is inactivated [395–397]. As the normal cell cycle

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approaches S phase, the Rb protein is in the nucleus bound to cellular transcription activator family proteins E2F. Adenoviral E1A protein binds to the Rb protein that releases E2F, making it available to induce transcription of cellular genes for DNA synthesis initiation—especially that of the viral DNA. The construct AdE2F is a carrier of the E2f gene. The virus is highly cytotoxic for human non–small-cell lung cancer cells. In Ad(E2F)-1RC, the E1A gene is under the control of the E2F-l promoter element. Quiescent normal cells do not express E2F, whereas tumor cells overexpress E2F and support viral replication with high efficiency [398–400]. The fusion protein encoded by a gene located in the viral genome between the E2F-binding Rb protein and the DNA-binding domain of E2F inhibits DNA replication. The gene for the fusion protein was placed under the promoter of p53 in the genome of the 01/PEME adenovirus construct (Canji) with deletion 1101 from its E1A sequence. Its inhibitory effect on p53 is therefore disabled [401]. As expected, this virus construct will not grow in normal cells expressing wild-type p53. The gene of the adenovirus protein E3–11.6K was placed under the control of the major late viral promoter to achieve an intensified late cytotoxic effect in tumor cells. 01/PEME in vitro and in xenografted human tumors surpasses the cytotoxicity of E1B- deleted dl 1520 viruses. CyclinD/CDK4 and CDK6 (cyclin-dependent kinases) phosphorylate the Rb protein, rendering it unable to arrest the cell cycle [396]. Both mutated cyclins and CDK can act as oncogenes, whereas CDK inhibitors such as p16 can act as tumor suppressors. When such CDK inhibitors are mutated (independently from adenoviral infection, as in many human tumors, such as melanoma, lymphoma, breast cancer, etc.), oncogenesis is promoted. The AdPML construct delivers an intact tumor suppressor gene, the one that is translocated in acute promyelocytic leukemia— t(15;17)—to breast carcinoma cells. These tumor cells failed to grow as xenografts in nude mice and showed cell cycle arrest at G1, decreased levels of cyclin D1 and CDK2, and increased p21 CDK-inhibitor activities. The Rb protein became dephosphorylated, making it able again to stop the cell cycle [402].


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The adenovirus receptor internalization and degradation protein [403] is anti-apoptotic. It antagonizes TNF-induced apoptosis and internalizes the Fas receptor, surrendering it to degradation within lysosomes. However, it also internalizes EGF-R, depriving a tumor cell of EGF-induced mitotic stimuli. The adenovirus proteins E1B (19K, 55K, 14.7K0) act as Bcl2 homologues and inhibit extrinsic apoptosis initiated from receptors Fas or TNF␣, activators of FADD (Fas-associating protein with death domain) but not of FLICE (FADD-like IL1␤ converting enzyme) [404]. E1B 14.7 antagonizes TNF␣. E1B55K inactivates p53 protein encoded by gene on chromosome 17p13. Whereas E1A increases the activity of p53 (proapoptotic events), the 55 kDa E1B and E4ORF6 proteins bind p53 at two sites, remove it from the nucleus and degrade it (anti-apoptotic events). One of the viral E4 gene product proteins, E4ORF4, causes apoptotic cell death independently from E1A or p53, unless counteracted by Bcl-2 or BclXL. Delivery of Fas ligand (L) or FADD protein genes by adenovirus constructs (Adeno-FL; Adeno-FADD) into human glioblastoma cells expressing Fas but resisting anti-Fas antibody-induced apoptosis rendered these cells highly prone to programmed cell death [405,406]. Many human tumors downregulate Fas receptor expression but express FasL and kill Fas CD95 receptor-positive defensive host immune T cells. Colon carcinoma cells expressing Fas receptor succumbed to programmed cell death upon intracellular expression of adenovirus-encoded FasL and attracted inflammatory cell infiltrations. Adenovirus-mediated transfer of FasL expressed internally, induced apoptotic death of prostatic carcinoma cells [407]. When transferred into endothelial cells by adenovirus, FasL inhibited neovascularization [408]. Adenovirus type 2 early transcription unit 3 protein 14.7ORF downregulates Fas receptor expression at the tumor cell surface, exerting its antiapoptotic effect [409,410]. The death domain containing protein p84N5 triggers apoptosis from within the nucleus; its gene N5, delivered by adenovirus AdN5, induced apoptosis in tissue cultures and xenografts of human tumors, but spared normal diploid fibroblasts [411,412].

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The Bcl-associated BAX is a pro-apoptotic member of the Bcl-2 family. Its gene is driven by vascular endothel growth factor (VEGF) overexpressed in lung cancer cells. The bax gene is incorporated into the adenoviral genome together with the VEGF promoter element to form the AdVEGFBAX construct, which induces apoptotic death of human lung cancer cells, whereas it spares normal bronchial epithelial cells that do not overexpress the VEGF gene [413]. Recombinant adenoviruses (rAd-EGFP) infecting dendritic cells elicit rapid antibody, NK, and immune T cell defensive reactions in the murine host, and MHC and costimulatory molecules also incease. Levels of cytokines, IL-6, IL-12p40, IL15, IFN␥ and TNF␣ rise, whereas IL-10, IL-12p35, and TGF␤ tend to decrease. Cytoplasmic NF-␬B rapidly translocates to the nucleus, a reaction inhibited by an adenovirus encoding a mutant I␬B␣ gene [389]. The adenovirus Ad.IkappaBM triggers apoptosis of hepatocytes, which is counteracted by Bcl-2, allowing for viral persistence through suppression of innate defensive reactions. Adenoviruses produce VA-RNA I to block PKR and escape the antiviral effect of IFN␣ [414,415] (similarly to NS1 of influenza virus, ␴3 protein of reovirus, and E3L and K3L proteins of VV). The E1A gene product protein suppresses malignant transformation mediated by the neu oncogene [416]; additional literature cited [417–419]. Of innumerable adenoviral constructs created for oncolytic activity, none emerges as being exclusively the best; the ONYX construct is a prototype that has been clinically tested most frequently. The dl1520 adenovirus (ONYX-015; CI-1042) (McCormick, in this volume; and extensively reviewed elsewhere [333,361,420–427]) replicates without its E1B gene and cannot produce its E1B55K protein (which would bind p53). Its E1B19K gene and its Bcl-2 homologue gene-product protein remain intact. In human malignant glioma xenografts ONYX is oncolytic independently from the p53 status of the tumors [428]. In head and neck squamous cell carcinomas, it induced major tumor regressions (additively to or synergistically with cisplatin and radiotherapy) [429,430]. Intraarterial administration of ONYX for the treatment of gastrointestinal adenocarcinomas metastatic to the liver in addition to 5-FU and


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leucovorin induced 11% PR and 37% MR with stabilization of disease [431]. Intratumoral injection of ONYX into hepatobiliary tumors induced 6 % PR and 56 % MR and stabilization of disease [432]. In a patient with adenocarcinoma of the gall bladder, it was proven by RT-PCR (real time polymerase chain reaction) aimed at viral hexon expression that the virus replicated in the injected host both in tumor and stromal cells [433]. Another E1B-55kDa-deleted adenovirus (YKL-1) killed human gastric carcinoma cells in a p53-independent manner; that is, even cancer cells with wild p53 still functional failed to resist viral replication. Possibly, loss of the alternative reading frame protein p14ARF also allows E1B 55 kDa-deleted adenoviruses to replicate, inasmuch as p14ARF interacts with Mdm2, the major antagonist of the p53 protein. E1B 19 kDa protein inhibits E1B 55 kDa protein-induced and p53-induced apoptosis. E1B 55 kDa-deleted adenoviruses (Ad-⌬E1B19; Ad⌬E1B19/55) exhibit greatly increased apoptosis-inducing efficacy and are awaiting clinical trials [434,435]. E1A exerts tumor-suppressive effects on the HER2/neu proto-oncogene with differentiation–induction, reduced metastatic potential, and increased susceptibility to TNF␣-induced apoptosis [436,437]. While E1A may act as an oncogene product protein in rodent cells, in contrast, in human cells it exerts tumor suppressive activity. Human rhabdo- and osteosarcoma cells, and lung and breast cancer cells transfected with retrovirally inserted E1a gene showed attenuation of their malignant phenotype and their growth rate was suppressed. Ad5dl01/07 produces a defective E1A protein and triggers a strong apoptotic response in infected tumor cells, thereby inhibiting the growth of xenografted human tumors. When the human tyrosinase promoter is used to replace the adenoviral E1A promoter in the viral genome, the genetically engineered adenovirus (AdTyr⌬24 and AdTyr⌬2⌬24) becomes highly cytotoxic for melanoma cells with a high yield of viral progeny in melanoma cells and low yield, if any, in other (control) cells [438–440]. Estrogen- and hypoxia-responsive promoters and telomerase transcriptase promoters of the E1a gene drive adenoviruses AdEHT2 and AdEHE2F in ERⳭ human breast cancer cells [400]. The E1a gene of the Delta24

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adenovirus with a 24 bp deletion codes for a protein that cannot inactivate the Rb protein in normal cells, disallowing viral replication. In Rb-defective cells, such as high-grade gliomas, the virus replicates without restraint. Ad5-Delta24 destroyed human glioma cells in the brains of nude mice without causing encephalitis. The Delta24 virus expresses arginine-glycine-aspartic acid (RGD) peptides for high affinity to ␣-integrins that are overexpressed in glioma cells. Delta24 is in clinical trial at the M.D. Anderson Cancer Center [441]. Ad E3 sequence encodes the adenovirus death protein activated at the end of the viral cycle to dissolve the cell and allow lateral dispersion of the new viral progeny [381]. The E3Ⳮ Ad5-⌬24RGD with deletion of base pairs 923 to 946 of the E1A sequence was much more cytotoxic for human cancer cells than its E3ⳮ variant. Ad5-⌬24RGD suppresses the growth of human glioma xenografts in nude mice and synergizes with radiotherapy. Adenoviruses with mutated E1a gene replicate only in tumor cells with E1A-like activity, such as in HeLa cells, undifferentiated embryonic carcinoma cells, or hepatocellular carcinoma cells. As shown at Baylor in Houston, TX, E1a-mutated adenoviruses destroyed hepatocellular carcinoma xenografts [442]. At this stage, it is not possible to omit and ignore any of the adenoviral constructs: One may score extraordinarily well in a future clinical trial. Intravenous (i.v.) infusion of ONYX-015 in combination with chemotherapy (irinotecan and 5-FU) and IL-2 induced both stabilization of disease and PR in patients with advanced malignancies as well as virus-neutralizing antibody production; however, virus particles accessed tumor masses. For patients with chemotherapy-refractory metastatic colorectal cancers, ONYX-015 stabilized the course of disease for 11 to18 weeks [443]. Of the attenuated replication-competent adenoviruses, agents CV706 E3ⳮ and CV787 E3Ⳮ destroy xenografted human prostatic carcinoma cells [444]. In these viruses, encoding of the E1A protein is under the direction of a PSA gene promoter-enhancer. Agent CV787 eradicated prostate cancer xenografts after one i.v. injection. Unlike Ad-sPSA-E1, replicating only in PSAⳭ tumor cells, Ad-hOC-E1 is under the pro-


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moter osteocalcin and it replicates also in PSAⳮ or PSAⳭ androgen-dependent and independent prostate cancer cells [445]. The replication-competent adenovirus Ad5-CD/TKrep inserts a fused HSV tk gene and a cytosine deaminase (CD) gene into the genome of transfected prostate cancer cells after direct injection of the virus into the tumors. Thereafter, patients receiving 5-fluorocytosine (5-FC) and ganciclovir experienced reduction of tumor size and a drop of PSA [446]. Posttreatment prostatic tumor biopsies showed extensive coagulation necrosis and two patients remained in CR 1 year after treatment. Metastatic androgen-resistant prostate cancer cells show extensive invaginations of their cell membrane, in contrast to healthy prostatic cells, which are free of this development. These tumor cells overproduce PSA, resist apoptosis, gain androgen-independence, or continue to use testosterone as a growth hormone and overexpress the gene cav-1 that encodes the proteins caveolae [447]. Tumors other than those of the prostate (breast, colon, and ovarian carcinomas) also overexpress caveolae and gain multiple drug resistance. Endothelial cells undergoing neoangiogenesis also overexpress caveolae and show extensive invaginations of their cell membranes. A murine promoter of the cav-1 gene was inserted into the genome of an adenovirus upstream to the HSV tk gene. Adcav-1tk was thus created. Upon treatment with ganciclovir, in these hosts orthotopically grafted with prostate cancer cells that were transfected with Adcav-1tk, massive necrosis of the tumor cells occurred. Human tumor cells not in S phase may escape cytotoxicity of the HSV tk gene-ganciclovir (TK-GCV) system; when overexpressed, however, adenoviral E1A protein drives the cell toward S phase and cell-killing efficacy of the TK-GCV system increases [448]. Ovarian carcinoma cells are often deficient in the expression of CAR. The Ad5/3luc1 virus possesses a chimeric Ad5 fiber protein with an Ad3 knob domain directed at the Ad3 integrin receptors, allowing it to enter CARⳮ ovarian carcinoma cells [449]. Another agent, Ad-⌬24RGD, readily infects the CARⳮ ovarian carcinoma cell through integrins. AdCMVHSV-TK delivers the tk gene (driven by CMV or Rous

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sarcoma virus promoters) into ovarian carcinoma cells and renders the tumor cells highly susceptible to ganciclovir [450]. The transmembrane protein CD40 appears overexpressed in many tumors, including ovarian carcinomas. Its natural ligand, CD154 of the TNF family, may induce a growth inhibitory effect [451]. The fusion protein CAR/G28 ligand targets CD40 and, when expressed in the construct Ad5luc1-CAR/ G28, it facilitates viral infection of ovarian carcinoma cells, which undergo apoptosis and gain increased susceptibility to cisplatin [452,453]. Good basic knowledge of cancer cell biology and congenial thinking led to the creation of these adenoviral constructs, which are poised to spring into wide clinical application. Adenoviral transfer of the HSV tk gene into anaplastic lymphoma cells renders these cells ganciclovir-sensitive [454]. Epstein-Barr virus immediate early protein encoding genes BZLF1 and BRLF1 convert the latent EBV state into lytic infection. Adenoviral vectors delivering these genes into EBVⳭ gastric carcinoma cells induced tumor cell lysis [455]. This type of intervention may possibly work in EBVⳭ lymphomas (African Burkitt’s lymphoma, Hodgkin’s disease, primary brain lymphoma in AIDS). Recombinant adenoviral vectors delivering HSVtk gene into human lung and other solid tumors, including adrenocortical carcinoma [456–458], sensitize the targeted tumor cells and some bystander cells to ganciclovir-mediated lysis. The aziridine-cyclobenzamide (CB1954) is converted by the Escherichia coli enzyme nitroimidazole reductase (NTR) into a cytotoxic alkylator. The delivery of the NTR gene by adenovirus into primary or metastatic liver tumors is expected to render these cells highly susceptible to i.v. (or intraarterial) administration of CB1954 [459]. Rabbit carboxylesterase (rCE) converts the camptothecin prodrug, irinotecan, into its cytotoxic metabolite. The rCE gene under the influence of the Rous sarcoma virus (RSV) promoter is delivered by AdRSVrCE into neuroblastoma cell, with tumor cell death occurring upon treatment with irinotecan [460]. This treatment spares CD34 stem cells and purges stem cell preparations (collected before high-dose myeloablative


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chemotherapy) of tumor cells before its reinfusion into patients for rescue. Ad-CMV-CD contains the cytosine deaminase (CD) transgene driven by a cytomegalovirus promoter; specifically, its protein product enzyme CD sensitizes breast cancer cells to 5-FC. This strategy has been proposed for purging bone marrow stem cell preparations, which are to be reinfused into patients after myeloablative high-dose chemotherapy [461]. Ad-CD vectors infect pancreatic and prostatic carcinoma cells. As few as 400 vector particles per cell render these cells highly susceptible to 5-FC [462,463]. Replication-competent adenoviral vectors carrying either L-plastin or CMV promoters for an inserted CD gene and for the viral E1A were designed to contain also an intraribosomal entry site (IRES) sequence (AdCMVCDIRESE1A; dLpCDIRESE1A). These constructs were cytotoxic for infected and for bystander human breast, ovarian, and colon cancer cells and FC increased cytotoxicity in an additive fashion, whereas normal parenchymal and stromal cells were spared [464]. Adenovirus 5 variant CV890 (Calydon, Sunnyvale, CA) is allowed to express both E1A and E1B from a single transcription response element whilst an encephalomyocarditis virus element regulates its internal ribosome entry site. An ␣-fetoprotein (AFP) enhancer-promoter element amplified from human genomic DNA drives its replication. In non-AFP-producer cells, there is minimal viral replication, but in AFPproducer cells, viral replication increases up to 105-fold. CV890 replicates to cytotoxicity in human hepatocellular carcinoma cells and synergizes with doxorubicin [465]. Adenovirus 5 CG8840 (Cell Genesys, San Francisco, CA) is attenuated and replication competent. Its E1A and E1B genes are driven by an uroplakin promoter deriving from the uroplakin gene UPII, which is specifically expressed only in cells of the urothelium. CG8840 replicates to cytotoxicity 104-fold better in transitional carcinoma cells of the urinary bladder than in glioma, melanoma, prostatic or ovarian carcinoma cells, or normal fibroblasts. The virus is effective in combination with docetaxel [466]. The clinical performance of these adenovirus constructs

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is expected to be highly additive, if not synergistic, to current treatment modalities for cancers of the genitourinary tract. Adenovirus vectors are constructed for the gene therapy of human cancers (mentioned frequently, but not reviewed in this volume; extensively reviewed elsewhere-[39-43, 333,361, 410,417-419]). Wild-type p53 gene adenovirally transferred into human tumors in vitro or in xenografts suppressed tumor growth or even induced apoptotic deaths of infected tumor cells, but in Phase I clinical trials, apart from inducing remissions in rare individual cases, no cures resulted. Stagnation (stabilization) of disease progression is the best result so far recorded. In glioblastoma, p53 mutations are not essential for the malignant transformation [467,468]. In head and neck squamous cell or nasopharyngeal carcinomas [469–471] and in lung cancers [472,473], synergism of adenoviral vectors carrying wild-type p53 with chemoradiotherapy is evident in xenografts [472] but not in clinical trials [473]. In breast cancer [474], reinsertion of wild-type p53 by adenoviral vector sensitized the tumor cells to TNF-induced apoptotic death. In prostate or urinary bladder carcinomas [475–479], intratumoral injections or intravesical instillations of adenoviral vectors armed with wild-type p53 show favorable clinical results [479]. Controversies between preclinical assays showing efficacy of viral vectors against human tumor xenografts, but limited performance of the same agents in subsequent clinical trials, call for further efforts to explain the reason for the discrepancy and to reconcile it in favor of successsful clinical trials [480,481]. For example, in a comparison of wild-type p53 and adenoviral death protein expression for killing lung cancer cells, the replicating Adp53rc performed better [482]. Therefore, replication-competent vectors should be favored, however, these vectors must remain harmless in normal tissues of the host. The actin-regulatory protein gelsolin is present in normal, but it is absent in cancerous epithelial cells. When the gelsolin gene was inserted by adenoviral vector Ad-GSN into the genome of human bladder cancer cells orthotopically xenografted into the bladders of nude mice, tumor growth was sup-


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pressed [483]. The construct Ad-RB94 inserts the gene of the truncated (short of 112 amino acids at its NH2 terminal) retinoblastoma protein p94 kDa into squamous cell carcinomas of the head and neck. Xenografts of these tumors failed to grow [484]. The PTEN (phosphatase on chromosome ten) tumor suppressor gene, when reinduced into prostatic cancinoma cells by an adenoviral vector, induced no tumor cell death, but blocked the metastatic potential of the tumor cells [485]. The gene of the IFN-inducible protein p202, when inserted into breast cancer cells by an adenoviral vector, rendered the tumor cells highly susceptible to TNF-induced apoptosis [486]. The cDNA of the oncoprotein p14ARF incorporated into an adenoviral vector infecting MCF-7 breast cancer cells sensitized the tumor cells to cisplatin [487]. Further efforts concern the delivery of lymphokine (IFNs and ILs) and cytokine (hematopoietic growth factors, such as GM-CSF) genes into tumor cells. Anti-neoangiogenesis (AdmEndo for endostatin) [488] genes, immunostimulatory co-factor (B7s, heat shock proteins; MHC) genes, cell suicide genes, or these genes combined in the same adenoviral vector (such as endostatin and tk genes for the treatment of renal cancer) and delivered into human tumors of all cell types follow suit. In many cases, the genes were shown to resume their normal function, directing the tumor cells toward differentiation or apoptotic death and increasing the tumor cells’ susceptibility to ionizing irradiation, to cytotoxic chemotherapy, or to immune attack by host antibodies, NK cells, and immune T cells [489]. Antigens released from apoptotic (but not from necrotic) tumor cells undergoing programmed cell death are re-expressed not in a tolerogenic but in an immunogenic manner by phagocytic macrophages and mature dendritic cells, thereby inducing a form of postoncolytic antitumor immunity [490–494]. What dangers and side effects do these new therapeutic measures entail, such as insertion of viral genes that may transactivate proto-oncogenes in the host cell? Pathogenicity of replication-competent viral agents may be regained due to recombination with a latent virus harbored in the host. What possible countermeasures might the tumor be able to mobilize

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to escape destruction by these new therapeutic interventions? It is apparent that no single intervention will kill out the entire tumor cell population in its natural environment (the tumorbearing host) and that combination therapy involving viral vectors with antitumor immunological attacks or chemoradiotherapy will be necessary for the induction of durable CR that may eventually lead to cure. Parvoviruses Parvoviruses are small, icosahedral particles containing a ssDNA linear genome of 5 kb with terminal palindromes. Whereas adenoviruses infect quiescent cells, parvoviruses require cells in the S phase of their cycle for replication. Secondstrand synthesis of the viral DNA and completion of a lytic infection of the cell are accomplished. The left viral gene driven by promoter P4 encodes nonstructural proteins NS1 and NS2 acting as nuclear phosphoproteins and regulators of viral capsid assembly; the right viral gene driven by promoter P38 encodes structural proteins VP1 and VP 2, forming the viral capsid. Autonomous parvoviruses do not require a helper virus for their replication. Dependoviruses, like the adenoassociated virus (AAV), integrate their genomes into host cell DNA sequences and lay dormant without causing disease until an unrelated helper virus (adeno- or herpes virus) superinfects the cell and induces the parvoviral genome to replicate itself [495–499]. Heather Mayor at the Melnick Department of Virology, Baylor University, Houston, TX, concluded that harboring some parvoviral genomes was ‘‘good for your health’’ [500], inasmuch as these agents suppress oncogenesis. But certainly not that of parvovirus B19: This is the causative agent of erythema infectiosum in children and induces hemolytic anemia with aplastic crisis in the bone marrow [501–505]. The possible association of parvoviruses as causally involved agents in rheumatoid arthritis [506] remains uninvestigated. Minute virus of mice (MVM) existing as prototype and immunosuppressive agents (MVMp and MVMi) are able to infect and kill human tumor cells. The MVMp autonomous par-


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vovirus destroys xenografts of human tumors. Armed with the anti-angiogenic chemokine, IP-10, this virus was shown to destroy human tumors formed by hemangiosarcoma or Kaposi’s sarcoma cells [507] (Rommelaere, in this volume). MVMp was able to transfect human tumor cells with the HSV tk gene and render them highly susceptible to ganciclovir [508]. The feline panleukopenia autonomous parvovirus retargeted by insertion of an integrin-binding peptide could infect the human rhabdomyosarcoma cell line Rh18A [509]. Mink plasmacytosis with hyper-gammaglobulinemia or Aleutian mink disease is caused by an autonomous parvovirus. Viral vaccines containing parvoviral capsid proteins VP1 or VP2 did not prevent but, rather, enhanced disease progression. Antibody-virus immune complexes enter macrophages through the Fc receptor; the virus is not neutralized and infects the macrophage. Vaccines incorporating the virally encoded nonstructural protein NS1 induced CD8 lymphocytes reactive with infected cells and provided partial protection [510–512]. Canine, feline, and porcine parvovirus vaccines are in use in veterinary medicine. In beagle dogs, venereal sarcomas regressed when the animals became infected with the canine parvovirus. Live attenuated feline panleukemia parvovirus vaccine could prevent the outgrowth of canine sarcomas but it was ineffective against established tumors [513]. The chicken anemia parvovirus encodes an apoptosis-inducing 121 amino acid protein, apoptin. This protein elicits p53-independent apoptosis and kills human osteogenic sarcoma and other human tumor cells in vitro [514]. A recombinant H1 parvovirus vector that encodes apoptin protein, a p53-independent and Bcl-2-insensitive apoptotic effector, was shown to act as an apoptosis-inducer but only in tumor cells and not in normal fibroblasts [515]. It remains to be determined whether certain myxo- and paramyxoviruses (influenza A virus; NDV), grown in embryonated chicken eggs that may harbor the chicken anemia parvovirus, exerted unusually fast apoptotic death of tumor cells instead of full replicative cycles because of this undetected contaminant [516].

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In the initial clinical tests carried out at Sloan-Kettering, the human autonomous parvovirus H1 was shown to cause viremia but was ineffective against disseminated sarcomas [517]. Later, it was shown that it destroyed human breast cancer [518] or melanoma cells and rendered infected melanoma cells more immunogenic through release of heat shock proteins (HSP72) [519]. Lymphocytes, monocytes, and dendritic cells resisted infection with H1. Hepatocellular carcinoma cells are susceptible to H1, whereas resting hepatocytes resisted infection [520]. The chemotactic CC chemokine protein-3 of monocytic origin (MCP-3), when expressed in tumor cells (osteosarcoma, mastocytoma), elicits Th1-type antitumor immune reactions in immunocompetent hosts. When H1 was used as a vector to deposit the MCP-3 gene in HeLa cells, xenografts of these MCP-3-transduced HeLa cells elicited NK cell- and macrophage-mediated immune reactions in nude mice, leading to rejection of the xenografts [521]. Attempts at the construction of an adenoviral E1A gene-carrier H1 parvovirus vector (H1Ad5E1A) for oncolytic virus therapy of human cancers have not been abandoned [516]. Autonomous parvovirus vectors possess a packaging capacity for foreign DNA sequences not much more than 4.8 kb [522]. The carrier state of AAV may result in suppression of naturally occurring tumors. This concept is deduced from serological data showing low titers of AAV antibodies in 15% of cancer patients, and higher titers in 34% of cancer-free individuals [523]. Women with or without squamous cell carcinoma of the uterine cervix, especially, displayed such differences. In this entity, there is an interplay between AAV and HPV. Human papilloma virus-16 E2 protein can activate latent AAV [524–527]. Therefore, if uterine cervical cells are undergoing malignant transformation by certain anogenital HPV strains and if these cells harbored latent AAV genomes, activation of AAV could result in the suppression of HPV-induced oncogenesis. However, when the dsDNA HPV genome integrates itself into host cell chromosomes, its E2 function is lost and AAV will not be activated. The malignant transformation of the cell will proceed unopposed. If the AAV carrier state involves the testicles, oligospermia and male infertility may result. Aden-


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oassociated virus infection of the female genitalia may contribute to spontaneous abortions [528]. Adenoassociated virus possesses 4700 to 5000 nucleotide bases and integrates preferentially into locus 19q13 [529,530]. Its genome accepts inserted foreign DNA sequences (clusters of differentiation CD antigens; neomycin phosphotransferase gene; cystic fibrosis transmembrane conductance regulator gene, etc.) elevating AAV to the rank of a very promising vector for gene therapy. Although adenoviral genomic sequences may persist in human lymphocytes, these cells, with or without prior adenoviral exposure, accept genomic insertions by an AAV [531–534]. Angiostatin gene carrier AAV was injected intramuscularly (one single injection) into nude mice harboring growing human glioblastoma xenografts in their brains. Mortality was 100% for untreated mice, but 40% of treated mice survived more than 10 months. Surviving mice secreted high levels of angiostatin in their blood over 250 days. Sacrificed animals showed inhibition of neoangiogenesis in the regressing brain tumors [535]. When activated, the AAV rep gene encodes multifunctional Rep proteins, including Rep68 and Rep78, that suppress mitoses of the cell. Rb proteins p107 and p130 also suppress cell divisions. Adenoviruses inactivate these proteins to initiate cell divisions. Cellular transcription factor YY1 [536], an antagonist of TGF␤, suppresses AAV Rep proteins and no transcription for AAV reproduction occurs. Adenovirus E1A interacts with YY1, and liberates Rep.Transcription of AAV for its reproduction is initiated. Human papilloma virus E2 protein also interacts with cellular YY1 and with Rep. Rep proteins also bind to E1A, therefore preventing phosphorylation (inactivation) of Rb proteins, which therefore do not dissociate from E2F, causing the cell cycle to remain arrested. Rep78 interacts with p53 protein and protects it from degradation. Rep proteins 52, 68 and 78 bind E1A. Intact E1A phosphorylates Rb and separates it from E2F. Cell divisions proceed under these conditions (dephosphorylated Rb bound to E2F would block cell divisions) [537]. Transformed cells with intact DNA repair mechanisms and with wild type p53 are resisant to parvovirus infection,

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whereas DNA repair-defective and p53-deficient cells are susceptible in accepting parvoviral entry and replication. Whereas H1 and AAV-5 do not increase cisplatin sensitivity of tumor cells, AAV-2 does; together they induce apoptosis, but through mitochondrial (endogenous) mechanisms (except in small-cell undifferentiated carcinoma of the lung) rather than through the FasL → Fas system [538]. HeLa cells harboring integrated AAV become more susceptible to gamma rays [539] and undergo apoptosis when treated with anti-Fas immune serum. During this process, the latent AAV is activated and its genomic sequences replicate [540]. Saos p53-null and Rb-null osteosarcoma cells die apoptotic death upon entry of AAV. In contrast, normal osteoblasts with wild p53 and intact Rb pause in G2 and resist AAV-induced death. When HPV-16 E6 protein degrades p53, AAV infection kills the cell. Apparently, the entry of a special DNA, like the AAV DNA with hairpin structures at both of its ends, induces cell death in tumor suppressor gene-defective cells but not in healthy cells [541]. The ‘‘Achilles heel of cancer’’ has purportedly been found [542]. Polio–Rhinovirus Recombinants The naked icosahedral ssRNA poliovirus (PV) enters through its receptor CD155 (PVR) by eliminating viral protein VP4 and exposing the hydrophobic viral structural protein VP1 to extrude from the virion’s surface as the virion passes through the cell membranes. Poliovirus receptor-related molecules include PRR-1 nectin-1, lymphocyte homing receptor CD44 (only when associated with PVR), and a heparan sulfate. The viral RNA of 7–8 kb is either extracted from the viral capsid in endosomes or is ejected by VP1 through the cell membrane into the cytosol. As a positive strand viral RNA, the poliovirus genome has dual functions. It is either copied into negative strands that serve as templates for the synthesis of positivestrand genomic RNAs and it enters the translational system to act as mRNA and encodes the formation of structural protein capsid pentameres that encapsidate the positive-strand genomic RNA. Poliovirus mRNA is uncapped and its translation


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occurs on internal ribosomes through IRES (internal ribosome entry sites), which are 400-nucleotide-long segments within the 5′nontranslated region of the viral genome. Translation occurs by binding of a 40S ribosomal subunit to IRES in a 5′independent and cap-independent manner. Internal ribosome entry sites also have the capacity to encode cell type-specific restrictions regulating viral propagation to occur [543–545]. Meanwhile, a cellular inhibitor of the RNA-activated serine-threonine PKR blocks IFN production. The PKR N-terminal is the regulatory domain activated by dsRNA. Its C-terminus is the catalytic domain. Poliovirus degrades PKR. Poliovirus protein 3A is anti-apoptotic, inasmuch as it inhibits TNF-induced apoptosis. Poliovirus proteases 2A and 3C, on the other hand, may trigger apoptotic death of the infected cell as they interact with the anti-apoptotic BclXL or pro-apoptotic BclXS. Within the cell (anterior horn motor cells of the spinal cord), PV proteins 2B, 2BC and 3A inhibit vesicular transport from the endoplasmic reticulum and disassemble the Golgi apparatus. Host cell protein translation is blocked and is replaced by viral protein translation. The N-S dipeptide is cleaved to liberate viral proteins VP2 and VP4 from VP0 and the viral proteases will not be incorporated into the mature virus particles. After VP0 cleavage, the viral genome is ‘‘spring-loaded’’ so as to be readily ejectable from the virions upon their entry into a new host cell. Infectious virions exit through the cell membrane within 8 hours after viral entry, resulting in cytoplasmic lysis of the cell [543]. Mutations in the 5′noncoding (untranslated) region (5′UTR) of the viral genome deprives the virus of its neurovirulence. P1Sabin was mutated in nucleotide 480, changing amino acid sequences in capsid proteins VP1, VP3, and VP4. P2Sabin was mutated in nucleotide 481 and VP1. These mutations revealed that domain V within the IRES of PV was the residence of the neurovirulence gene; later it was found that domains V and VI are coordinately responsible for the neurovirulence of the wild PV. P3Sabin was mutated in nucleotide 472 and VP3. Poliovirus P3/119 isolated from a case of vaccine-

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associated poliomyelitis was a revertant from P3Sabin to P3/ Leon [543]. The family Picornaviridae incorporates the genera Enterovirus (with PV included) and Rhinovirus. Minor and major rhinoviruses enter host cells through Ig-like ICAM and lowdensity lipoprotein and sialic acid receptors. Polio- and rhinoviruses exhibit canyons in their capsids. In the case of rhinoviruses, ICAM domains penetrate deep into these canyons [543]. Virus-neutralizing antibodies also intrude into the canyons. Internal ribosome entry site elements of these two genera are closely related, form type 1 IRES elements, and are interchangeable between members of the two genera. Human rhinovirus type 2 (HRV2) IRES is devoid of neuroxicity-encoding elements and it could replace PV type 1 (Mahoney) IRES elements; thus the chimeric virus PV1(RIPO) was created (see in this volume). Poliovirus 1(RIPO) does not replicate in neuroblastoma cells or in cells of neuronal origin, but grows well in HeLa cells. It infects the skeletal musculature of CD155 transgenic mice but exerts no neurotoxicity in them; it is not neurotoxic in Cynomolgus monkeys upon intraspinal injection. If HRV2 receives IRES domains V and VI from PV1Mahoney, the parent virus of PV1(RIPO), however, it starts replicating in neuroblastoma cells and gains neurovirulence in CD155 transgenic mice. Human glioma and neuroectodermal tumor cells express CD155. Human glioblastoma xenografts in athymic mice were completely eradicated after a single intratumoral injection of PV1(RIPO) (Melinda Merrill, D. Solecki and M. Gromeier, in this volume) [546–550]. SAFETY MEASURES AND REGULATIONS The ideal oncolytic virus should not cause disease in the tumor-bearing host. It should not integrate in the host cell genome (unless it is a retroviral vector intentionally delivering a gene). Preferably, it should not be excreted in urine and saliva, so it should not spread in the patient’s environment. It should be genetically stable, to avoid recombination, multiplicity reactivation, and other means for regaining virulence upon


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encounter with a latent, related or unrelated virus carried by the tumor-bearing host or existing in the patient’s domicile. If the oncolytic virus is excreted, it should not be readily infectious in healthy human beings. It would be most advantageous if a genetic switch-off function could be incorporated into the viral genome to curtail unwanted replication of the oncolytic virus in the patients. Ideally, the virus should be highly tumorselective, sparing normal healthy cells and replicating exclusively in tumor cells. The oncolytic virus should not be highly immunogenic (rather, it should be ‘‘tolerogenic’’). It would not be without additional risk-taking if oncolytic virus therapy were to be combined with immunosuppressive measures. The candidate virus for virotherapy should derive from safe sources. Tissue cultures, serum preparations, and other ingredients can be contaminated with exo- or endogenous avian or mammalian retroviruses; potentially oncogenic simian viruses (SV40), such as in the first preparations of Salk and Sabin poliovirus vaccines and in an adenovirus vaccine; latent herpes viruses; porcine parvoviruses (in trypsin preparations); or hepatitis A or B viruses (in an early formulation of yellow fever vaccine stabilized with human sera). Bacterial contaminants must be excluded; especially frequent are mycoplasma contaminations of tissue culture preparations. Finally, the viral preparations should be endotoxin-free. Some cartilage samples taken from cadavers and transplanted into joints were found to be contaminated with Clostridia and caused fatal septicemias in the recipients. The facility where the virus preparations are produced should be licensed, properly staffed with qualified and experienced personnel, and equipped with a filtered air supply. Special attention should be given to the use of high-quality and controlled ingredients. The indiscriminate use of human sera (except the patients’ own blood products) should be prohibited to avoid use of oncolytic viral preparations containing hepatitis viruses, HIV-1, prions of Creutzfeld-Jakob disease, and other contaminants. The facility should follow approved manufacturing instructions. The premises should be supervised and periodically inspected by the licensing authority to assure

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that the required and agreed upon manufacturing procedures resulting in a clinically administered oncolytic virus preparation are meticulously observed. Record keeping should be thoroughly accurate so that batches issued would be clearly identifiable (for urgent withdrawal from use in case of trouble). The product should be distributed in a safe manner, so that the quality of the preparation would not diminish because of inappropriate transportation. Good guidelines for manufacturing practices are available [551,552]. The risk–benefit ratio must be clearly explained to the patient in the approved informed consent forms. Patients with treatment-refractory advanced cancers may accept higher risks than patients with cancers potentially curable by means other than oncolytic virus therapy. The risk–benefit ratio of competing treatment modalities should be presented to the patient in a balanced and honest manner before selecting an oncolytic virus for therapy. Qualified staff of physicians and nurses, preferably specialty board-certified in hematology-oncology and infectious diseases, should attend the patients. Clinical records and documents should be kept and preserved according to guidelines of good clinical practice. The approved investigational protocols should not be administered in private offices. Preferably, academic institutions or well-administered non-private, non-profit hospitals should take charge of the clinical testing of oncolytic viruses. The Institutional Review Board should exercise rigorous supervision over the conduct of these clinical trials. Recitations of anecdotal case histories and inviting patient testimonials should be discouraged. Premature media publicity should be scrupulously avoided. Media publicity should be allowed only for proven results and always with moderation. The principal investigator’s announcement should be followed by comments from independent experts (in good taste and in good faith). Verily, gross exaggerations and distortion of facts should not be tolerated or awarded by casual and indiscriminate citations in the literature without criticism being exercised. Financial involvement of the principal investigators should be discouraged or declared and promotional maneuvers for the sale of the product during its investiga-


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tional period of work (Phase I and II clinical trials) should be prohibited. THE FUTURE Will naturally oncolytic or genetically engineered viruses be the best clinically useful oncolytic agents? Will antiviral host immunity be detrimental (antibodies neutralizing the oncolytic virus) or promotional, with NK cells practicing antibodydirected cellular cytotoxicity (ADCC) against virally infected tumor cells? Can oncolytic viruses be combined with each other simultaneously or sequentially, or with other therapeutic interventions, such as chemotherapy, monoclonal antibodies and immunotoxins, inhibitors of oncogene- or fusion oncoproteinassociated tyrosine kinases, or antisense oligonucleotides (see in this volume)? Will viruses contribute further to the efficacy of cancer vaccines—to viral oncolysates made with reo- or vesicular stomatitis (VS) viruses, or to dendritic cell vaccines in which x-ray–inactivated tumor cells are fused with mature live autologous dendritic cells and the fusion is mediated by a viral fusion protein (NDV, Sendai, VSV)? Would lipid-encapsulated nonpathogenic but oncolytic viruses [553–557] be taken up preferentially by voraciously feeding cancer cells, whereas the encapsulated virus would not infect normal cells through the customary viral envelope or capsid to cell receptor pathway? Polymer-coated [558,559], cationic liposome-conjugated [555,556], or microbead-conjugated adenovirus preparations [560] are already being tested for oncolytic viral therapy. Target tumor cells of low viral permissivity yield to microbeadconjugated adenoviruses, accepting them readily [560]. The M. D. Anderson Cancer Center tested a cationic liposome-encapsulated E1A gene preparation for the treatment of breast and ovarian carcinomas [556]. Perhaps the antiviral antibody response, which may be detrimental to oncolysis in cases of repeated viral inoculations, may be suppressed or averted in this way? Are three-dimensional organotypic multicellular spheroids more reliable models than refined tissue cultures (deprived of stromal cells) or xenografts for preclinical testing of oncolytic viruses [561]?

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AFTERTHOUGHTS Viral invasion of the host elicits prompt innate and subsequent adaptive immune reactions. These immune reactions differ, if the virus is a virulent one, from those mobilized against an attenuated live viral vaccine. In the first case, the virus overcomes IFN production [562,563]; neutralizes other lympho-, cyto- and chemokines by encoding soluble decoy receptors for them [64,564–567]; escapes neutralization by antibodies in producing quasi species particles [568]; kills dendritic cells, macrophages, and immune T cells [569]; evades NK cells [570]; and suppresses the presentation of its antigens in an immunogenic fashion [571–573]. Many viruses are able to prevent immediate apoptotic death of infected host cells to secure the full maturation of their entire progeny [574,575]. Alternatively, these virulent pathogens may kill the host or evoke tolerance to establish a carrier state of viral latency without causing any morbidity (HSV-1, HSV-2; zoster virus; EBV). In contrast, the attenuated virus induces the production of virus-neutralizing antibodies and immune T cells with the persistence of appropriate memory cells to effectively overcome subsequent infections by the virulent virus of the same species. The relation of a host with, or its immune reactions to, replication-competent or genetically modified oncolytic viruses is unnatural, very complex and the least well understood. Indeed, both attenuated (rabies) and virulent viruses (measles) have induced rare remissions of malignant tumors in patients. Although viral infection of patients with cancer is not unusual, the rarity of this phenomenon—that is, remission of cancer coincidentally with a natural viral infection—is conspicuous. Although oncolytic viruses have the capacity to prolong or spare the lives of cancer patients, these attenuated or genetically modified viruses may be less endowed for the evasion of host immunity and succumb to it rapidly, allowing partially lysed tumors to re-grow. For example, pre-existing immunity to adenovirus type 5 (Ad5) hampers its usefulness in protocols for viral oncolysis or gene therapy, whereas viral toxicity may prevail even in immune individuals. In contrast, Ad35 is much less immunogenic in human communities, pre-existing immu-


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nity to Ad5 does not neutralize Ad35, and Ad35 constructs readily insert transgenes into human cells [576]. The situation with retro(lenti)viral vectors is even more complex. The DTA lentiviral vector delivers the diphtheria toxin A gene into human prostatic carcinoma cells and kills the tumor cells (in xenografts) [577]. However, work with replication-competent retro(lenti)viral vectors is subject to the infidelity of reverse transcription, mistakes at the transgene insertion, suppressed or altered transgene expression, and difficulties in tagging gene-modified cells, especially when nerve growth factor receptor technology is used for this purpose. The host’s immune surveillance system is not overlooking the genetically engineered retro(lenti)virus; innate and adaptive immune reactions may eliminate the virus upon its repeated inoculations. In the murine or human hematopoietic systems, retroviral insertion may unexpectedly induce apoptosis, differentiation or clonal expansion of the infected cell population. Manipulation of the NGFR during retroviral insertion induced clonal expansion of monocytes, culminating in monocytic leukemia, in the mouse. It is not yet known what leukemogenic genes might have been inadvertently transactivated in a child receiving successful gene therapy for X-linked SCID by retroviral gene transfer in France [578]. Thus, the ideal oncolytic virus or viral vector has not as yet been identified. Work with enteroviruses at the August Kirchenstein Institute in Riga, Latvia and in the former Soviet Union more than 30 years ago for the virotherapy of human cancers [12,13] now reveals that these viruses induced apoptosis in the infected cells [579]. This event would result in incomplete oncolysis and explains the rapid regrowth of most virally infected tumors. If the cell dies immediately after viral entry, there will be no mature virions produced to propagate viral oncolysis within the tumor. However, tumor apoptosomes could induce antitumor immunity mediated by DC. Mediators of this ‘‘postoncolytic immunity’’ could attack virally not-infected tumor cells as well [580]. First, the innate NK cells and, later, the immune T cells are mobilized to kill tumor cells by cytoplasmic lysis with perforins or antibodies

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(in an ADCC reaction with NK cells) or by nuclear clumping (programmed cell death; apoptosis) through cascades emanating from ‘‘death receptors and ligands’’ from the cell membrane. Conventional immune surveillance predating the appearance of the tumor is attributed to patrolling NK cells [581]. This is the cell population that responded first in patients to immunization with VOs. Natural T cell immune responses to tumor-associated antigens arise after the inception of the tumor and appear to co-exist in vivo with advancing tumors, contrary to the case with in vitro assays, which show that these T cell clones are able to expand and to kill autologous tumor cells [582]. Large, granular and smaller, more compact lymphocytes were shown to kill allogeneic and autologous tumor cells more than 30 years ago (J. G. Sinkovics, Chapter 2 in this volume) [149], but their characterization, the identification of the antigens (TAA) with which they react, and their use for adoptive immunotherapy did not materialize until recently. Preventive (VO) [134] and therapeutic (DC) cancer vaccines induce clonal expansion of these T cell populations. Even vaccination against growth factors (VEGF and VEGF-R; bFGF) that induce neoangiogenesis could result in tumor regression [583]. Subverted macrophages are frequently enlisted to produce cytokines or chemokines that act as paracrine growth factors for certain tumor cells [584]. Some viruses (influenza, measles, vaccinia) infect and may kill macrophages; others (NDV) activate macrophages (for the advantage or disadvantage of the host, as the individual case may be) (V. Schirrmacher, Chapter 4 in this volume). However, in case of intact macrophages, the ADCC reaction may be mobilized, as macrophages, through their FcR, capture antibody-coated tumor cells with cognate immunoglobulins attached to tumor antigen epitopes, and engulf and digest them. What immunomodulators (BCG scarified over the site of VO injections 30 years ago; GM-CSF administered in the past few years; lipid encapsulated viral constructs engulfed by macrophages in 2004) would activate the macrophage to kill the tumor cell and avoid being subverted by it? Viruses evoke cytokines [585] that may act against the tumor (TNF␣; IFN-


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␣␤␥ IL-2, IL-12; Fas ligand) or may induce cytokines (IL-10), rendering the host tolerant toward the same tumor antigens that the virus was supposed to co-immunize against. Certain virally induced lympho- and cytokines may be those that the tumor had already expropriated for its own auto- or paracrine growth loops. Some melanoma cells use the IL-2 → IL-2R loop and even FasL→Fas a circuit to induce mitosis; some neuroblastoma cells are driven by the TNF␣→TNF␣R loop. Interleukin-6 is a growth factor for multiple myeloma, Kaposi’s sarcoma, and kidney and some prostate carcinoma cells; IFN␥ is a growth factor for Kaposi’s sarcoma and certain osteogenic sarcoma cells (reviewed by Sinkovics in this volume). Paracrine (of keratinocyte origin) IL-7 drives the growth of Se`zary cells in mycosis fungoides [586–588]. Adenovirally (AdCAIL2) mediated delivery of IL-2 into prostatic carcinoma cells has been accomplished. Interferon-␥- and IL-4-secreting T cells invaded the transfected tumors and induced tumor cell death, while PSA levels dropped in the patients’ blood [589]. The IL2 gene-carrier vaccinia virus VVIL-2, deriving from xenogeneic culture, infected immature dendritic cells, which matured, expressed CD80, CD86, and MHC class II antigens and started to secrete IL-12. When VVIL-2 derived from syngeneic cultures, the infected DC did not produce IL-12; instead they secreted IL-10 and TNF␣ [590]. Thus, DC can induce, alternatingly, immunity or tolerance. The major suppressor of DC maturation and activation is IL-21, a relative of IL-4 and IL15 [591]. A refined technology can be envisioned in which the oncolytic virus would be given with IL-21 and the host would tolerate it, whereas TAA would be processed by mature DC for IL-2 and IL-12 production and for immunogenic presentation to T cells. In mice, the genetically engineered (rVSV)IFN␤ acted as an attenuated, tolerated, and highly oncolytic agent [592], but it has not as yet been tested against human tumors. The effect of virally induced chemokines on tumor growth is still a terra incognita. Antiviral or other antibodies, such as those resulting from Th2-type immune response, may complex with the antigenic epitopes by coating them. These concealed antigens, that would be otherwise targeted by cytotoxic T cells, may escape this type of immune attack. Some

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lymphocyte subclones of tumor-bearing mice could accelerate tumor growth [241,593–598]. No tumor enhancement has been as yet reported in patients as a consequence of oncolytic virus therapy; did it occur and remained unreported? The task remains to find systems in which oncolytic viruses persist until total oncolysis is achieved, regardless of the mechanism—apoptosis; cytolysis caused by host immunity directed at immature viral particles and tumor antigens coexpressed; or by the outburst of a fully mature viral progeny, thus lysing the tumor cell, but without morbidity [599–601]. Promising systems to achieve these effects are those in which fusogenic viruses induce tumor cell syncytia (NDV, VSV, HSV, in this volume) and spread within them without being exposed to virus-neutralizing antibodies; or those of dendritic cells, which phagocytize apoptotic tumor cells and co-express viral and tumoral epitopes to immune T cells (as in viral oncolysates). Influenza virus-infected macrophages are engulfed by dendritic cells that induce T cell-mediated immunity directed against virally infected cells [602]. If the virally infected apoptotic cell is a tumor cell, this mechanism of antigen presentation may explain the antitumor efficacy of the first influenza viral oncolysates (Sinkovics, in this volume). The crystal structure of the human class II MHC protein HLA-DR1 complexed with an influenza virus peptide is a phenomenal sight [603] and the structure is of high immunogenicity. Could we envision that viral and tumoral antigenic epitopes are co-expressed in the same fashion in viral oncolysates? In patients immunized with viral oncolysates, we should be able to visualize the ‘‘immunological synapse’’ between professional antigen-presenting cells (mature dendritic cells), as antigenic peptide epitopes of viral and tumoral origin are co-expressed in the grove of MHC molecules for presentation to T cell receptors next to co-stimulatory mediators (B7.2, IL-2, and IL-12) [604], which are necessary for breaking the tolerance to, and for the initiation of, a sustained Th1-type antitumor immune reaction of therapeutic strength. However, immunological synapses can be formed between dendritic cells and B lymhocytes, which are representatives of Th2-type im-


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mune reactions. Inhibitory NK cells also form their immunological synapses [605], in which case the target will be spared. Further, NKT cells arise in the tumor-bearing host and are guided by their receptors (KIRs; NKp30,44, 46; NKG2D) to transformed cells to act as agents of antitumor surveillance [606]. When the placenta established itself in the ancestors of mammals some 300 million years ago, it must have compromised the, by then fully operational, adaptive immune system. The VDJ hypermutations and their initiators, the retrotransposon-derived RAG1 and RAG2 systems, originated in the ancestors of cartilaginous fishes (Chondrichthyes) some 450 millions years ago [607–609]. This compromise consists of the forced acceptance of paternal antigens expressed by the semi-allograft fetus. The trophoblast, but especially the syncytiotrophoblast, is an invasive and metastasis-prone entity. Its stem cells proliferate under the effect of fibroblast growth factors [610] (frequently used also by tumor cells in their autocrine or paracrine growth loops). The syncytiotrophoblast expresses syncytin [611], a HER-W retrovirally encoded fusion protein, in addition to hCG and TGF␤ (a Th3-type reaction) and interacts with temporarily activated c-myc and jun protooncogenes. It suppresses expanding maternal T cell clones, and expresses FasL to kill Fas receptor-positive maternal lymphocytes [612,613]. The phylogenetic origin of NK cells descends way back to the Botryllus urochordates [614]. It is surmised that ancient NK cells exerted antiviral defense, but it is proven that urochordate NK cells prevent incompatible fusion of host cell colonies. Some of their ancestral receptors appear to remain preserved throughout evolution, up to the species Homo. Maternal NKT cells emerged for the containment of the fetal trophoblast [615–617]. Since then, closely related NKT cell populations operate in the tumor-bearing host for the containment of invasive and metastatic tumor cells [618–620]. The placenta temporarily activates the proto-oncogenes and evasive reactions that tumor cells display constitutively. Placental proto-oncogenes are not mutated, whereas in the tumor, mutated, truncated, translocated, and fused oncogenes operate. Tumor-specific T cell memory can be generated after NK

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cell-mediated tumor rejection [621]. A virally infected tumor cell would be a primary target of NKT cells of the host. Preparations of LAK cells consist of subclasses of NK cells. Could LAK cells be enriched of NKT cells, if collected after immunization of the donor with oncolytic viruses or with viral oncolysates? The ‘‘immunological synapse’’ and NKT cells were the subject matters of discussions at the 56th Annual Symposium on Fundamental Cancer Research, ‘‘Cancer Immunity: Challenges for the Next Decade,’’ at the University of Texas M.D. Anderson Cancer Center, Houston, TX, October 14–17, 2003) [622]. In the pregnant woman T and/or NK cell, clones emerge to suppress maternal immune reactions to paternal antigens expressed by the fetus [623,624]; if they fail, the fetus is lost [625,626]. Pregnancy carried to term is supported by Th2-type immune reactions of the mother; Th1-type reactions lead to fetal loss [625]. In analogy, Th2-type reactions in a tumorbearing host promote the tumor, whereas the induction of Th1type reactions could lead to tumor rejection. When tumor cells secrete fetal antigens (AFP; hCG; CEA; CA-15-3; CA-125, CA19-9, etc.), would these substances activate similar classes of suppressor cells for the protection of the tumor (as another analogy of immune evasion as practiced both by the placenta and malignant tumors)? Would multiple pregnancies alter the woman’s susceptibility to subsequent neoplasms [627]? The rapidly expanding clone of the newly emerging suppressor cells could be decimated by low-dose cyclophosphamide [109] co-administered with an oncolytic virus. If molecular virology and molecular immunology unite, this unison may overcome expanding tumor cell populations. REFERENCES 1. Kovaćs F. Zur Frage der Beeinflussung des leuka¨mischen Krankheitsbildes durch complicirende Infectionskrankheiten Wien Klin Wochenschr 1893; 6:701–704. 2. Dock G. The influence of complicating diseases upon leuk+mia Am J Med Sci 1904; 127:563–592.


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2 New Biological Therapeutics COMPETITORS OR COLLABORATORS OF VIRAL THERAPY FOR HUMAN CANCERS

JOSEPH G. SINKOVICS Cancer Institute, St. Joseph’s Hospital; Departments of Medicine and Medical Microbiology-Immunology, The University of South Florida College of Medicine; The H. Lee Moffitt Cancer Center Tampa, FL

INTRODUCTION There is an explosive and close to overwhelming array of preclinical and actual Phase I and Phase II clinical trials of biological agents for the therapy of human cancers. A new era of cancer therapeutics is taking its long-awaited place. At the cutting edge are naturally occurring attenuated and geneti149

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cally engineered oncolytic viruses and viral vectors for gene therapy. Put in context, viral therapy of human cancers, tried and abandoned decades ago, re-emerges now to occupy a respectable position among these trials, even when the most sophisticated protocols of gene therapy with viral vectors [especially those with retro(lenti)viral vectors] are dealt with separately (regretfully not detailed in this volume, although we mention in this text some of the viral vectors that insert genes into the genome of cancer cells). Pre-clinical testing for viral therapy of human cancers is quite similar to procedures in use for all other biotherapeutical agents: tumor cell killing in vitro in tissue cultures and in vivo in xenografted human tumors. Even the results are quite similar: extraordinary success for high levels of tumor cell killing in these pre-clinical tests; disappointingly weak results in Phase I and Phase II clinical trials; long stabilizations of disease commonly achieved. However, there are most favorable exceptions of success: imatinib mesylate (Gleevec, Novartis Pharmaceuticals, East Hanover, NJ) for chronic myelogenous leukemia (CML); bortezomib (Velcade, Millennium Pharmaceuticals, Cambridge, MA) for myeloma; erlotinib (Tarceva, Genentech, South San Francisco, CA; OSI Pharmaceuticals; and Roche) and bevacizumab (Avastin; Genentech) for non–small-cell lung cancers [Eastern Cooperative Oncology Group (ECOG) and M.D. Anderson Cancer Center protocols] [American Society of Clinical Oncologists (ASCO) 噛2521, 2003; Physicians Desk Reference, 2004]. The Discussion includes comments on several treatment modalities (monoclonal antibodies and immunotoxins, preventive and therapeutic cancer vaccines, adoptive immune lymphocyte therapeutics, etc.) that may compete or co-operate with the virus therapy of cancer. The scope of this volume is not to review tumor immunology and immunotherapy, but because these disciplines overlap with the virus therapy of cancer, it is incumbent upon the contributing authors not to leave these connections unnoticed. This chapter provides a much-abbreviated cross section of these new biological therapeutic trials and seeks out the place where viral therapy of human cancers could fit in, either

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in competition, or in collaboration with, other new promising biotherapeutical agents. Of many pathological entities under investigation for the possible application of new biological treatment modalities, two—multiple myeloma and glioblastoma multiforme—have been selected to be reviewed here, inasmuch as they remain incurable and are targeted for oncolytic viral therapy. FARNESYL TRANSFERASE INHIBITORS c-ras* The ras family of proto-oncogenes first revealed itself when Kirsten† and Harvey** rat sarcoma (ras) retroviruses yielded these genes transduced by these viruses from their host cells [1–3]. Later, point-mutated human ras genes were found in transitional cell carcinoma of the urinary bladder and, thereafter, in a very large number of diverse human cancers. In an early analysis of malignant human tumors, the incidences of mutations of p53 and the K-ras gene were 50% and 41%, respectively. The specific target of tobacco smoke for mutation induction is codon 12 of the K-ras proto-oncogene. This mutation is more common in lung adeno- than in lung squamous cell carcinomas. In lung adenocarcinomas, mutations in codon 12 K-ras exceed 50% [4–7]. In colon adenocarcinomagenesis, K-ras mutations occur very early and are followed by 5qⳮ (the locus of the adenomatous polyposis coli APC gene at 5q21), 18qⳮ (the locus of the deletion in the colorectal carcinoma DCC gene), and 17ⳮ (the locus of p53) deletion. After K-ras and p53 mutations (or p53 deletion) occur, the patient’s prognosis worsens [7–11].

*

Italics indicate the gene (bcl-2); capital letters (Bcl-2; BCL-2) designate the gene product protein. ** The author had the privilege to become a friend of Dr. Werner Kirsten† in Chicago, IL in the late 1950s and worked at the same Section of Virology at M.D. Anderson Hospital in Houston, TX, where Dr. Jennifer Harvey spent a year of her fellowship in the late 1960s. † Deceased

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Co-operating with mutated K-ras in colorectal carcinoma cells, ␤-catenin translocates into the nucleus, initiates its own oncogenic cascade, and aggravates the prognosis [12]. K-rasmutated colon carcinoma cells circulate in the blood and reach the bone marrow [13]. Co-mutations of K-ras and APC genes are frequent (27%), whereas co-mutations of K-ras and p53 genes are rare (6.6%); single mutations of one of these genes are the most common (38.7%) [10,11].The autosomal dominant hereditary nonpolyposis colorectal cancer (Lynch syndrome) arises because of the failure of DNA mismatch repair genes (hMLH1,2,3,6) [14,15]. In pancreatic ductal adenocarcinomas, K-ras mutations are frequent [16,17]. Mutated K-ras gene product proteins elicit CD4 T lymphocytic infiltrates in the periductal pancreatic tissues [18]. In head and neck squamous cell carcinomas mutated K-ras is rare, but amplified wild Kras is overexpressed [19]. R-ras (a subclass in the H-ras family) is active in squamous carcinoma cells of the uterine cervix and promotes tumor cell proliferation and migration but is sensitive to inhibition by LY294002 (Calbiochem) [20]. The Ras association domain family 1A gene (RASSF1A) exerts suppressor effects on mutated ras; its locus is at 3p21, from which it is frequently eliminated (3 short arm deleted) in uterine cervical carcinomas. Human papilloma virus (HPV)-16 and HPV-18 possess transforming genes: E6 degrades p53; E7 inactivates Rb. In squamous cell carcinomas of the uterine cervix, HPVs are present in 90% or more of the cases; in adenocarcinomas of the uterine cervix, HPV presence stands at 50% [21,22]. The tumor suppressor gene RASSF1A (locus at 3p21.3) may be inactivated by promoter hypermethylation or by the loss of its hetero- or homozygosity (deletions). The intact RASSF1A protein binds GTP-Ras but hypermethylated RASSF1A is inactive. In 24% of cervical adenocarcinomas and 10% of cervical squamous cell carcinomas, RASSF1A is hypermethylated. Correlation of RASSF1A methylation and the presence of human papilloma virus (HPV) is uncertain, as if HPV-infected cervical epithelial cells advanced to malignant transformation without need for RASSF1A inactivation [22].


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Whereas MAPK activation by Ras correlates with the progression of hormone refractory disease in prostate cancer, the anti-androgen bicalutamide (Casodex, AstraZeneca, Wilmington, DE) inhibits anchorage-dependent cell growth and Ras signaling [23,24]. Experimental introduction of N-ras into CD34 stem cells resulted in the clinical picture of myelodysplasia. H-ras, K-ras, and N-ras mutations occur in patients with acute myelogenous leukemia (AML) infrequently (15%–30%) and mainly in patients who were occupationally exposed to potentially carcinogenic chemicals; involvement of H-ras in the cause of chronic leukemias (CLL; CML) appears to be insignificant [25–27]. N-ras codon 61 mutations occur early and persist in melanoma cells and result in deeper invasions. In familial melanoma, germline mutations of the CDKN2A/ARF (cyclinedependent kinase/alternative reading frame) and CDK4 chromosomal regions (at 9p21 and 12q13) are passed on; the very same melanoma cells also display somatic (ultraviolet light-induced) N-ras and BRAF mutations. The cascade emanating from a mutated N-ras gene involves the proto-oncogene raf and terminates through serine-threonine kinase activity in MAPK (mitogene activated protein kinase) cascade: the RASRAF-MAPK pathway. In melanoma cells, the BRAF protein exhibits amino acid substitutions (V599E or V599R or V599K) consequentially to somatic mutations in exon 15 of the gene [28–33]. When the RAF cascade goes toward the MEK/ERK (mitogen activated protein/extracellular signal-regulated kinase) pathway, the cell will upregulate its adenoviral receptor CAR, presumably rendering these tumor cells more susceptible to adenoviral oncolysis [34–36]. The raf kinase inhibitor BAY43-9006 is in clinical trials for the treatment of melanoma; early reports indicate that partial remissions (PR) and disease stabilizations were induced. The wild-type K- or H-ras genomic sequences encode their protein products that anchor themselves at the inner aspect of the cell membrane and on intracellular compartment membranes and are recruited into action when certain growth factor receptors (GF-R) capture their cognate ligands: epidermal (EGF-R); platelet-derived (PDGF-R); and HER2neu/Erb2

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(HER for human epidermal receptor). In healthy cells, the guanine diphosphate (GDP)-Ras protein complex is inactive and in ‘‘off’’ position and is active in the ‘‘on’’ position. Guanine triphosphate (GTP)-Ras dephosphorylates a double-stranded RNA-activated protein kinase (PKR), thus creating an interferon (IFN)-free environment favorable for the full replication of certain viruses (vide infra) in the cell so afflicted. In healthy cells, Ras and extracellular signal-regulated kinases (ERK) and protein kinase C (PKC) cooperate in immune cell and mast cell activation [37]. The ras→Ras cascade activates a number of proto-oncogenes and neoangiogenesis factors downstream and suppresses Fas receptor (cluster of differentiation, CD95) expression, thereby providing exemption from one form of apoptosis for the cell. It would be of considerable interest if Fas ligand (FasL) overexpression also occurred in these cells, in that, armed with FasL, these ras-mutated cells could kill CD95positive defensive host lymphocytes (unpublished). Among the proto-oncogenes activated by GTP-Ras is c-raf, encoding a serine-threonine kinase acting in unison with the mitogen-activated protein kinase (MAPK) system. Mutated B-Raf proteins are frequently detectable in melanoma and colon carcinoma cells. Physiological activation of Ras is reversible, but when point-mutated Ras and Raf-1 are constitutively active, the cells harboring them assume malignant phenotype. Ras mediates radioresistance through phosphatidylinositol 3-kinase (PI3K) and initiates Raf-dependent activities working within the MAPK pathway. Raf-1 may be activated independently from Ras by Bcl-2 and by protein kinase C (vide infra). Further, activated Ras acts upon the cytoskeleton’s relationship with the intercellular matrix and its cell adhesion molecules and integrins; consequentially, ras-mutated cells exercise increased locomotion and invasiveness. Wild-type neuroblastoma N-ras may exert a tumor suppressor-effect against murine thymic lymphomas, but mutated N-ras becomes oncogenic. N-ras regulates lymphoid and myeloid cell homeostasis, but N-ras knockout mouse embryos develop normally, whereas K-ras knockout mouse embryos fail to reach normal


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maturation [38]. Trans-farnesylthiosalicylic acid (FTS) is a Nras antagonist. Under physiological conditions, GTP-Ras converts into the inactive GDP-Ras by hydrolysis because of interaction with guanine nucleotide exchange factor (GEF). For point-mutated (most frequently at codons 12, 13, 61) ras gene product proteins, hydrolysis does not take effect and GTP-Ras remains constitutively activated in the ‘‘on’’ position [1–3]. Up-regulated peroxisome proliferator-activated nuclear receptors (PPARs) exert anti-inflammatory effects in macrophages [39–41]; suppress tumor growth, especially PPAR␥ in K-ras–driven tumor cells by inhibiting PI3K/Akt and cyclinD1 expression; and may induce terminal differentiation of human tumor (liposarcoma) cells: Troglitazone (TGZ) attachment to PPAR␥ induced this differentiation process. When PPARs capture their ligand, they emit pro-apoptotic signals in human breast and prostate carcinoma cells. A PPAR-agonist ␥-ligand (such as pioglitazone, sigma) inhibited ras-mediated malignant transformation and induced apoptosis in numerous cultured human cancer cell lines and synergized with histone deacetylase inhibitors. Ligands (TGZ) of PPAR␥ are in use to treat Type II diabetes, to induce regression of precancerous lesions in the upper digestive tract, and increase the efficacy of combination chemotherapy for metastatic cancers (AACR 2003 Symposium I by Eva Szabo of the National Cancer Institute). HER2 upregulates PPAR␥ in breast cancer cells but reduces its responsiveness to its ligands; trastuzumab (Herceptin, Genentech) neutralizes HER2 and synergizes with TZG in inbiting growth or inducing apoptosis of breast cancer cells [41]. PPAR␦ is upregulated by K-ras and activated by prostaglandins, products of cyclooxygenase-2 (see Part II). In the multistep model of colonic adenocarcinomagenesis, the adenomatous polyposis coli APC (5q21), K-ras (12p), p53 (17p13), and the human homologue of the murine double minute mdm (12q13-14) genes mutate sequentially, and E3 ubiquitin ligase MDM2 degrades the p53 protein (the ‘‘guardian of the genome’’). An antisense oligonucleotide (see Part III) directed to neutralize translation of the mdm-2 gene spares the integrity of p53 [42]. Mutated K-ras (glycine to valine sub-

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stitution at codon 12) is overrepresented in Duke’s C tumors, suggesting that K-ras contributes to tumor progression through lymph node metastases [4]. Viral Attack; Host Counterattack It now appears that ras-mutated malignant cells support the replication of certain viruses [influenza virus, Newcastle disease virus (NDV), reovirus, vesicular stomatitis virus (VSV)] to the full maturation of the viral progeny, resulting in bursting death attributable to lysis of the tumor cells. Nonmalignant counterparts of these cells protect themselves and neighboring cells with IFN production and resist the replication of these viruses. Whereas replication-competent wild or attenuated NDV strains accomplish the full maturation of their progeny by inhibiting innate IFN production, the incompletely replicating Ulster strain NDV induces IFN production [43]; replication-competent NDV strains are oncolytic by apoptosis induction or by bursting tumor cells, whereas replication-incompetent NDV strains are oncolytic by eliciting innate and adaptive humoral and cell-mediated immune reactions of the host directed against infected cells expressing viral and tumoral antigens co-jointly. These two processes of oncolysis may overlap; for example, when epitopes of apoptosomes of tumor cells are re-expressed by host dendritic cells (DC), or when the replication-competent virus somehow fails to suppress innate host reactions, such as IFN production. These viruses therefore emerge as selectively oncolytic agents ready for clinical trials. In human cell lines, genetically engineered so that they express the simian paramyxovirus 5 V protein, the STAT system (Figures 1 and 2) is subjected to proteasome-mediated degradation. In these IFN-free cell lines, viruses replicate uninhibited [44]. Wild-type influenza A viruses abound in nature, especially in avian reservoirs [45] and readily recombine with each other, so an attenuated live influenza virus may re-emerge as a pathogenic recombinant. Influenza A and B strains initially overcome host defenses by their NS1A and NS1B proteins [46]. Viral neuraminidase (HN) activates NK cell receptors NKp44 and NKp46 and


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Figure 1 The activated STAT system decisively contributes, if not to the initiation, certainly to the sustained maintenance of the malignant geno- and phenotype of the cancer cell. Until now, targeting STATs for cancer therapy received lower priority than other targets, such as the EGF-R/HER2 or the Bcl-2 anti-apoptotic systems. However, at the University of South Florida H. L. Moffitt Cancer Center, Tampa, FL, STAT receives the attention it deserves. (These illustrations are gratefully acknowledged as the courtesy of Drs. Richard Jove and Hua Yu. Reprinted with permission from Nature Reviews Cancer, February 2004.)

induces cytotoxicity against infected cells; but when new class I MHC molecules are generated in the infected cells and bind the killer cell immunoglobulin (Ig)-like receptor 2 domain long tail 1 of NK cells (KIR2DL1), cell killing is inhibited and the viral progeny can mature [47]. From the point of view of influenza viral oncolysates (VO), it is of paramount importance that nonimmunogenic and even tolerogenic proteins (ovalbumin) generate antibody and immune CD4 and CD8 responses in hosts infected with influenza viruses [48]; probably in the tumor-bearing host, tolerogenic tumor epitopes become immunogenic when presented within influenza VO. The oncolytic virus elicits antiviral immune reactions in the inoculated host. A three-dimensional mathematical model of a tumor infected by a replication-competent virus indicates

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Figure 2 The activated STAT system decisively contributes, if not to the initiation, certainly to the sustained maintenance of the malignant geno- and phenotype of the cancer cell. Until now, targeting STATs for cancer therapy received lower priority than other targets, such as the EGF-R/HER2 or the Bcl-2 anti-apoptotic systems. However, at the University of South Florida H. L. Moffitt Cancer Center, Tampa, FL, STAT receives the attention it deserves. (These illustrations are gratefully acknowledged as the courtesy of Drs. Richard Jove and Hua Yu. Reprinted with permission from Nature Reviews Cancer, February 2004.)

high chances for tumor escape because of immediately mobilized innate and subsequent adaptive immune reactions [49]. Some early cytokine reactions may promote tumor cell growth. The CXC chemokine IL-8 is pro-angiogenic and is prominently expressed in transitional cells of the urinary bladder; it may even act in an autocrine growth loop in these tumors. When NF␬B is liberated from its inhibitor I␬B, it translocates to the nucleus, where it transactivates the IL-8 gene [50]. Virus-neutralizing antibodies may eliminate the virus (an unfavorable event for oncolysis), or the replicating virus may produce ‘‘quasi-species’’ new progeny [51,52] and escape neutralization. Some viruses may exist complexed with antibodies; these immune complexes may be deposited in synovial membranes and kidney glomeruli. Antiviral antibodies reacting with tumor cells expressing viral antigens may evoke the


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ADCC reaction by enlisting NK cells or macrophages in reacting with their FcRs, and thereby inducing tumor cell lysis. Virally infected cells induce NK cell and immune T cell reactions (a most favorable event for oncolysis), but viruses may escape immune T cells [53,54] and viral peptide antigen may become tolerogenic [55]. When immunological synapses are formed between DC and lymphocytes, a subclass of NK cells or T cells may misconstrue instructions so received and become tolerogenic or immune-suppressive agents [56], an unfavorable event for oncolysis. Under such circumstances, immune reactions engendered by viral peptide epitopes may promote tumor growth (such as ‘‘enhancing antibodies’’). T cell interactions with virally infected or transformed cells are very complex, inasmuch as viral peptides may become tolerogenic; or tumor cells armed with FasL may kill immune T cells [57]. Regulatory and CD4 CD25 suppressor T cells (Tr; Ts) rule over tolerance vs. immune reactions [58–61]. Viruses switching on the ‘‘burglar alarm’’ upon entering a cell induce programmed cell death, often mediated by TNF␣, whereby no new mature viral progeny can be formed; in response, viruses evolved or expropriated genes encoding proteins inhibitory to apoptosis. Cells dying apoptotic death are engulfed by macrophages or load their antigens onto DC MHC type II molecules [62,63] to present them to CD4 helper lymphocytes. Endogenously processed epitopes are presented by MHC type I molecules to CD8 cytotoxic lymphocytes. If these antigens are expressed by mature DC, not in a tolerogenic (with IL-10), but in an immunogenic fashion (with co-stimulatory molecules B7.2, IL-2, IL12), they may elicit extremely strong immune reactions capable of lysing gross established tumors (a most favorable event). Viruses potentially oncogenic in the human host [human papilloma virus (HPV), Epstein-Barr virus (EBV), hepatitis B virus (HBV)] excel in overcoming host defense reactions at many levels and prevail [64], but malignant transformation by adenoviral E1a and ras, simian virus 40 (SV40), and HPV was inhibited by adeno-associated virus (AAV) Rep78-expressing plasmids, which preserve phosphorylated Rb and inhibit protein kinase A (PKA) when they arrest the cell cycle [65]. Protein kinase A is activated by luteinizing hormone in endo-

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metrial cancer cells and increases tumor cell invasiveness; in breast cancer cells, PKA and p38 intensified paclitaxel-induced apoptosis [66,67]. The dephosphorylated and inactivated nonstructural protein NS1 of minute virus of mice regains its helicase activity when co-incubated with protein kinase C, which is overactive in transformed cells, allowing parvovirus replication and genomic integration to take place preferentially in malignant cells. Adeno-associated viruses integrate their genomes into host cell chromosomes (AAV-2 to locus 19q13.3), inhibit mRNA and transcription of adenoviral gene E2a, readily penetrate solid tumors, inhibit neoangiogenesis by transferring the endostatin gene (rAA-HuEndo) into tumor-bearing hosts, and are elevated to the rank of good candidates for cancer gene therapy [68–74]. When an attenuated and replicating or, for gene therapy, genetically engineered, replication-competent or replicationrestricted (to selected cells, such as organ-specifically targeted tumor cells) virus infects a tumor-bearing host, it is quite unpredictable whether the host could eliminate it or the virus manages to evade its disposal. Mixtures of replication-competent and incompetent viral particles in the inoculum (for example VSV inocula) profoundly influence the host’s immune response [75]. Would suppression of antibody-mediated immune reactions (cytarabine; anti-B cell monoclonal antibodies) and promotion of Th1-type cytotoxic T cell reactions (IL-2, IL-12) directed against virally infected host cells tilt the balance in favor of viral oncolysis? A Sindbis virus replicon containing herpesviral gene VP22 and HPV-16 E7 gene induces E7-protein-specific CD8 cytotoxic lymphocyte-mediated immune reactions against HPV-infected cells [76]. Although human reoviruses are quite apathogenic in adult tumor-bearing and immunocompetent mice [77], infected newborn mice succumb to encephalitis with apoptotic death of nerve cells [78]. Hopefully immunosuppressed patients with cancer will not suffer any pathogenic effect of oncolytic reoviruses. Prior to the mobilization of elements of adaptive immunity in response to a viral infection, innate immune reactions are immediately activated, with an upsurge of lympho-, cyto-, and chemokines. The mammalian CXC chemokine family con-


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sists of 16 ligands and six receptors [79]. Some chemokines are inhibitory to tumor cells: Macrophage inflammatory protein-1␣/CCL3 and macrophage-derived chemokine CCL22 inhibit cell divisions and invite infiltration of macrophages, neutrophil leukocytes, T and NK lymphocytes and DCs into tumors that express these chemokines. Whereas the macrophage-inhibitory cytokine-1 (MIC-1) expressed by gastric cancer cells increased the invasiveness of the tumor cells, it made them susceptible to the MAPK inhibitor PD98059 (Calbiochem). However, tumor cells recruit many defensive and other cytokines (IFNs, ILs, TNFs, FasL, G- and GM-CSF, stromalderived GF, PDGF, ligands for EGF or HER2/neu, etc.) to promote their mitoses in autocrine and paracrine growth loops (Sinkovics, in this volume). In their native microenvironment, some tumor cell subpopulations may undergo rapid replication driven by the cytokines of the innate immune response; other tumor cell populations, especially those exposed to the oncolytic virus after their extrication from their microenvironment (in tissue cultures; in xenografts), succumb to the shower of cytokines or die because of the absence of some growth-supportive cytokines (see Part IV). Some viruses encode immunosuppressive cytokines (decoy IL-10) or soluble receptors for immunostimulatory cytokines (IFN-␥; anti-apoptotic serpins) and thereby neutralize them [80–89]. These extremely complicated interactions between virus and host are known at least in the case of oncolytic viruses. Attenuated measles virus-specific lymphocytes persist longer than antibody production after vaccination [90]; if the oncolytic measles virus elicited a similar reaction that would favor the tumor-bearing host and delay elimination of the oncolytic virus by antibody. Wild measles virus suppresses Janus kinase 1 (JAK1) phosphorylation induced by IFN-␣ and abolishes the IFN-induced antiviral state; IFN-␥ is not inhibited [91]. Although the influenza A viral NS1 protein is essential for the inhibition of IFN response of the infected cell, it is instrumental for the induction of immune T cells [92]. Influenza A virus could activate tumor antigenspecific (HER2/neu) cytotoxic lymphocytes, supporting the rationale for viral oncolysates as cancer vaccines (Sinkovics, in this volume). In mice devoid of mature B cells and antibodies,

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immune T cells could clear influenza A viral infection [93], an event most favorable for the tumor-bearing host when its tumor cells are infected with an oncolytic influenza A virus. When oncolytic viruses (influenza, NDV, reovirus, VSV) multiply to their full maturation in host cells with constitutively activated GTP Ras and with defective IFN response because if inactivated PKR [94,96], their oncolytic efficacy should match or surpass that of farnesyl transferase (FT) inhibitors for the selection of these viruses in clinical trials. The inhibitors have an advantage over the virus in that they do not induce an immune reaction that would neutralize them in the host. However, these enzyme inhibitors now also in clinical trials do suppress the malignant phenotype of ras-mutated cells. Would this intervention restore resistance of these cells toward the oncolytic virus or, to the contrary, if the two interventions were combined (enzyme inhibitors and oncolytic viruses administered simultaneously or sequentially), could they act additively or synergistically? The FT inhibitor R115777 (vide infra) failed to exert any antitumor activity in patients with pancreatic adenocarcinoma. In contrast, reovirus serotype 3 readily destroys cell cultures and xenografts of human pancreatic adenocarcinoma cells; here the oncolytic virus promises better results. A Raf kinase inhibitor is undergoing clinical trials in patients with metastatic colorectal carinoma; BAY43-9006 also inhibits ERK, induces long stabilizations of disease, and lends itself to combination with standard chemotherapy. In three clinical trials, orally administered BAY43-9006 induced 2 partial remissions (PR) in 114 patients with metastatic cancers (2%); stopped disease progression in 42 patients (stabilization of disease, 37%), but allowed disease progression in 37 patients (32%); 33 patients remain on treatment with stable disease for further evaluation; of 60 patients with metastatic colorectal cancers, disease stabilization occurred in 25 (42%) [97]. Could reovirus match these results; or could it improve these results if administered in combination with BAY43-9006? Adenoviral Oncolysis Some adenoviruses borrow their oncolytic potency from herpesviruses. Herpesviral replicons (G207, HE7tk) either render


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infected cells (melanoma; hepatocellular carcinoma) antigenic in the host of origin and elicit T cell-mediated immune reactions or insert the tk gene into tumors of the brain or into tumors of other organs, sensitizing the tumor cells (and some bystander cells) to ganciclovir [98–101]. Adenoviruses are used as gene vectors (not discussed but occasionally mentioned in this volume; well reviewed elsewhere) [102–109]. The transfer of wild-type p53 by retro- or adenoviral vectors by direct repeated injections into lung cancers revealed minor and partial responses occurring despite antiviral antibody production in the patients; on rare occasions (in one patient with bronchioalveolar carcinoma) intratumoral injections of viral vector of p53 resulted in partial regression of noninjected distant (brain, liver) metastases (ASCO 噛487a 2000). Adenoviruses are subjected to gene deletions; ONYX-015 or dl1520 has its E1B55 deleted and is supposed to favor for its replication p53-defective tumor (pancreatic and hepatocellular carcinoma) cells [110–112]. In 27 patients with metastatic colon cancer, dl1520 given through the hepatic artery with 5FU given intravenously (i.v.) induced seven responses (PR, MR) and nine stabilizations of disease occurred, whereas 11 patients continued to progress [103]. Adenoviral vectors Ar6pAE2fE3F or Ar6pAE2fF (with or without E3 region) are expected to attack Rb-defective (tumor) cells, where the viral E1A depends on overexpressed cellular E2F1 promoter [113–115]. The entry of Ad5 into tumor cells underexpressing the entry-site receptor CAR could be promoted if Ad5 possessed serotype 3 knobs [116,117]. Adenoviral E1A protein sensitizes cells to TNF␣, but AdTRAIL expressing a ligand kills not only hepatocellular carcinoma cells, but also normal hepatocytes [118,119]. CV890 AvE1a04i replicates only in hepatocellular carcinoma cells that are overexpressing the ␣FP promoter; CN706 and CV767 exercise prostate-specific expression of their E3 region and are aimed to grow in prostatic carcinoma cells [120–122]. Adenoviruses with deleted E1b genes (Ad-⌬E1B19.55) do not express the 19kDa or 55kDa proteins that protect infected cells from apoptosis and are highly apoptotic for infected tumor cells. Ewing sarcoma xenografts are susceptible to Ad-E1A gene therapy which increases tumor

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cell sensitivity to VP16 (etoposide) [123]. Liposome-encapsulated E1A gene therapy is in clinical trials for lung, breast, and ovarian carcinoma [124]. AdmRTVP-1 carries the proapoptotic mouse gene RTVP-1; it inhibits neoangiogenesis and elicits macrophage, DC, and immune CD8 T cell infiltrations into infected tumors. Adenoviruses can deliver tumor suppressor genes into tumor (colon carcinoma) cells: p16INK4/ CDKN2p16, the cyclin-dependent kinase inhibitor, or p53 into bladder or lung cancer cells and SCH58500 into ovarian carcinoma cells or BRCA1 into breast and ovarian carcinoma cell lines [125–129]. The N5 gene encodes the death domain protein p84N5, which triggers apoptosis from within the nucleus even when the cell is resistant to p53 therapy [130]. The protein NK4 is a structurally related antagonist of hepatocyte growth factor and, when expressed in AdNK4, it suppresses the growth of xenografted human pancreatic adenocarcinoma cells in the peritoneal cavity of mice [131,132]. Ad-IGF-IR/950 and /482 introduce an insulinlike growth factor antisense sequence into tumor cells and inhibit tumor cell divisions; tumor cells so affected may undergo apoptotic death [133]. Preoperative intratumoral (prostate cancer) injection of AdIL-2 vector resulted in inflammatory reactions, tumor necrosis, and falling PSA levels [134]. Adenovirally delivered IL-12 gene encodes the cytokine and promotes the development of Th1-type immune reactions [135]. When adenoviruses deliver the herpesviral tk and endostatin (ES) genes into brain tumor cells or into xenografts of human kidney cancer cells, the tumor cells become vulnerable to ganciclovir and bystander cells may also be killed [136]. The IL-11 receptor ␣-locus chemokine CCL27 gene inserted into the genome of ovarian carcinoma cells by Ad-RGD-mILC worked to induce immune T and NK cell reactions, rejecting the tumor xenografts in immunocompetent mice [137]. AxdAdB-3 has mutated E1A and deleted E1B, and it is unable to react with p53. E1A-mutated or deleted adenoviruses are unable to bind Rb protein; AxdAdB3 selectively replicated in, and was cytotoxic to, gall bladder carcinoma xenografts [138]. Ad-TRAIL, carrier of the gene encoding the TNF-related apoptosis-inducing ligand, induced apoptotic death of the infected cancer cells and exerted a by-


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stander effect in tumor cells in the vicinity of infected cells [118,119]. Malignant glioma cells with homozygous p16 gene deletion accepted infection with Ad-p16, experienced cell cycle arrest, and underwent senescence. The gene product protein p16INK4a is a cyclin D1-dependent kinase inhibitor, preventing phosphorylation of the Rb protein (the cell cycle stands still in G1); the p14ARF gene product protein counteracts the effects of the proto-oncogene MDM2: p53 escapes MDM2 binding and is not degraded by the ubiquitin-proteasome pathway. In human tumors, the gene for INK4a/ARF (alternative reading frame) at locus 9p21 is frequently mutated or deleted, removing the brake from the cell cycle and exempting the cell from p53-induced apoptosis. The p53 gene inserted into the genome of tumor cells by Ad-p53 is protected from degradation by coinfection of the same cell by Ad-ARF; human lung cancer cell xenografts doubly infected in nu/nu mice die programmed cell death as induced by p53 [139,140]. In hormone- and multiple– drug-resistant prostate cancer cells, NF-␬B is constitutively activated and translocates to the nucleus unopposed, an antiapoptotic event; adenovirus pAxCAmI␬B-M expressing the negative dominant I␬B super-repressor abrogates NF-␬B activation and restores the tumor cell’s susceptibility to apoptosis induction by chemotherapeuticals (paclitaxel) in both androgen-sensitive and androgen-insensitive prostatic carcinoma cell lines [141]. Canji’s adenovirus 01PEME has its E1a gene and its E3 region deleted and has a p53-responsive promoter (to drive E2F antagonist E2F-Rb) and a late promoter inserted. It is unable to replicate in normal cells but reaches very high titers in human tumor cells, even after i.v. inoculations [142]. Cancer cells operate with reactivated telomerase reverse transcriptase (hTERT). Adenovirus hTERT-Ad expresses the gene of E1A protein under the control of the hTERT promoter and replicates best in hTERT-overexpresing tumor cells; it is more cytopathic in xenografted human tumor cells than ONYX-015, even when p53 is intact [143]. The histone deacetylase inhibitor FR901228 induces cell-surface overexpression of CAR and ␣v integrins; in these cells, transgene insertion by AdCMV␤gal was most efficient [144]. Cyclooxygenase (COX)-

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2 gene expression is very low in normal cells but is increased in tumor cells. COX-2 gene-driven adenoviral E1A gene facilitates viral replication best in ras-mutated and MAPK-overactive tumor cells [145,146]. Replication-defective and survivin gene-carrier adenoviral vector (Ad-survivin) and a phosphorylation-defective Thr34→Ala survivin gene-carrier adenoviral vector (pAd-T34A) protected and destroyed capillary networks of human breast cancer xenografts, respectively; pAd-T34A induced mitochondrial apoptosis with cytochrome C release, resulting in apoptotic death of both endothelial and tumor cells [147,148]. The CD154→CD40 activation stimulates antigen presentation; adenovirally (Ad-CD154) inserted CD154 gene upregulates ␣v integrin expression in murine lymphoma cells and augments their immunogenicity [149]. ONYX-411 replicates in tumor cells in which the Rb protein is inactivated, E2F is deregulated, and the cell cycle rolls forward uninhibited [152]. Tumor necrosis factor (TNF)-␣ is antagonized by NF␬B and c-FLIP, the inhibitor of caspase 8. Adenoviral protein E1A sensitizes cells to TNF␣ and antagonizes both c- and v-FLIPs, sending them to ubiquitin/proteasome-mediated degradation [151]. An immunoconjugate-encoding adenoviral construct induces tumor cells to overproduce the immunoconjugate directed at factor VIII of endothelial cells of the tumor bed; as neovasculature is destroyed, the tumor regresses [152]. The combination of replication-defective (without E1A, E1B, and E3 transcription units) and replication-competent (such as ONYX-051 without E1B55K protein) adenoviral vectors, which overexpress adenoviral death protein, synergize in killing human lung and liver cancer cell xenografts [153] (Table 1). Adenoviral vectors induce humoral and cell-mediated immune reactions in the infected hosts and are quickly eliminated, or cannot be repeatedly and effectively used. Polyethylene glycol-coated or liposome-encapsulated viral vectors are less immunogenic; corticosteroid- or budesonide-treated hosts are less immunoreactive. Some host tissues can be rendered tolerant to the viral vector (whereas other tissues of the same host remain immunoreactive); the vector may carry immunosuppressive genes prohibiting antigenic expression by MHC


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Table 1 Principles of Viral Engineering for Virotherapy Virus Ad.CAR-EGF⌬24 Ad5⌬24RGD AdenoCV706 AdenoCV890 AdenoCG884 AdTyr⌬24 AdEHT2 ONYX-015

Adeno01/PEME Ad-ARF

Adenovirus Delta24

Ad(E2F)-1RC Adeno-FL; AdenoFADD Adeno VEGF BAX Adenovirus hTERT Ad-CMV-CD

HSV1 G92A HSV1DF 3834.5

Effect EGF-R-overexpressing tumor cells are attacked Viral entry into CAR tumor cells through integrins Replicates in prostate cancer cells under the effect of PSA promoter Replicates in ␣FP (fetoprotein)-expressing hepatocellular carcinoma cells Replicates under the uroplakin promoter expressed by transitional cancer cells of the urinary bladder Tyrosinase promoter in melanoma cells drives viral replication to cytotoxicity Hypoxia-responsive/estrogen responsive promoters drive viral replication in breast cancer cells E1b gene-deleted, E1B55K protein-deprived adenovirus replicates in p53-deficient tumor cells Attacks cancer cells with mutated/lost p53 Protects wild-type or virally inserted p53 from degradation in proteasomes by antagonizing MDM2 through insertion of gene for p14ARF Deprived of gene product protein that inactivates Rb in normal cells; it cannot grow in normal cells; replicates in RB-deficient (glioma) cells E2F tumor cells support viral replication; no viral replication in E2F quiescent cells Delivers Fas ligand into tumor cells expressing CD95 Fas receptor, inducing apoptosis VEGF promoter drives expression of pro-apoptotic BAX in lung cancer cells Its E1A protein is under the control of the hTERT promoter in telomerase-preserving tumor cells Inserts cytosine deaminase transgene under CMV (cytomegalovirus) promoter into breast cancer cells, where the encoded enzyme renders the prodrug 5-fluorocytosine cytotoxic Replicates under albumin promoter in hepatocellular carcinoma cells Replicates preferentially in MUC-expressing pancreatic carcinoma cells

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class I molecules to CD8 lymphocytes; not adeno- but less antigenic adeno-associated or retrolentiviral vectors may be used [154–156]; or anti-B or -T cell monoclonal antodies are to be co-administered. Farnsyl Transferase Inhibitors One major enzyme family responsible for Ras activation is that of the FT; inhibitors of these enzymes defuse the cascade. For example, the very high incidence of breast and salivary gland carcinomas in the ras-transgenic ‘‘oncomice’’ is reduced to a minimal occurrence by FT inhibitors [157]. Posttranslational modifications of the Ras protein consist of farnesylation (addition of farnesyl lipid group to Ras isoform proteins by FT, a zinc metalloenzyme heterodimer); phrenylation (covalent addition by thioether linkage of 15-C farnesyl or 20-C geranylgeranyl group to C-terminal cysteine residues); and geranylgeranylation [158–163]. These events are now targeted by enzyme inhibitors that have already passed pre-clinical testing in vitro (in tissue cultures) and in vivo (in xenografted human tumors) and are in Phase I or Phase II clinical trials. The chemical structures of FT inhibitors are well depicted in a particular article from the University of Florida at Gainesville [164]. Among the competitors or collaborators of ras-mutation–dependent oncolytic viruses, FT inhibitors occupy an important position. SCH66336 (lonafarnib, Sarasar, ScheringPlough) is a non-peptidomimetic CAAX (C ⳱ cysteine; AA ⳱ aliphatic amino acids leucine, isoleucine, valine; X ⳱ methionine, serine, glutamine, leucine) inhibitor of FT. This compound inhibited in vitro growth of Hras-mutated human tumor cells (especially when the wild-type p53 was preserved) and suppressed the growth of xenografted bcl2-abl-mutated leukemic cells. In Phase I clinical trials, it induced only 1 PR in 44 patients with non–small-cell lung cancer (NSCLC) and other solid tumors; provided no survival benefit to patients with colorectal or pancreatic carcinomas; and was toxic when 400 mg twice daily dosage was exceeded, but in lower nontoxic dosage it synergized with taxanes and cisplatin. Tested against human melanoma cell lines in vitro, lonafarnib ex-


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erted antiproliferative and pro-apoptotic effects and synergized with cisplatin. Tested against PhⳭ CML cell lines in vitro, lonafarnib acted additively with imatinib or cytosine arabinoside but daunorubicin or etoposide antagonized its efficacy. In squamous carcinoma cells, SCH66336 inhibited AKT; adenoviral vector expressing constitutively active act reversed this effect [165–169]. R115777 (tipifarnib; Zarnestra, Janssen Pharmaceutica Products, Titusville, NJ; Ortho Biotech, Bridgewater, NJ) is a nonpeptidomimetic quinolone-derived inhibitor of FT on CAAX. It prevents benzopyrene-induced lung cancer development in mice [170]. When tested in patients with acute myelogenous leukemia (AML), 8 clinical responses occurred in 25 patients (32%) and two responses were complete remissions (CR). More recently, 10 of 30 elderly patients with AML responded to R115777 and 8 of these responses were CR; there was hematologic toxicity associated with remission induction. Of 36 patients with acute leukemias, 10 clinical responses occurred and 2 were CR. In myelodysplasia, 2 of 16 patients experienced CR. Chronic myelogenous leukemic (CML) patients in blast crisis also responded. This compound could clear leukemic blast cells from bone marrow in vitro before its reinfusion into patients, who received myeloablative high-dose chemotherapy [171–175]. Some patients with colon cancer responded with a drop of CEA levels. Human colon cancer cell lines may acquire resistance to tipifarnib; the resistant cell line remained sensitive to chemotherapeuticals, the phosphatidylinositol 3′kinase (PI3K) inhibitor LY294002, and the EGF-R tyrosine kinase inhibitor PD153035, which inhibit xenografted human cancer cell growth, whereas R115777 is quite inactive against pancreatic cancer cells. R115777-resistant colon cancer cells remain sensitive to etoposide, platinol, paclitaxel, and MAPK/ ERK inhibitor UO126 or PI3K inhibitor LY294002 [176]. In comparison, 18 patients with metastatic colorectal adenocarcinoma received i.v. ONYX-015 E1B55kD gene-deleted replication-selective adenovirus; only in 4 patients was disease stabilization observed for 2 to 4 months and eventually all patients progressed [102]. In 30 patients with advanced cancers treated with tipifarnib, 1 complete remission (CR) and 8 PR were

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recorded, at the price of hematologic, gastrointestinal, and dermatologic toxicities. Of 28 patients with advanced solid tumors, stabilization of disease occurred in 3 cases. This compound in patients with pancreatic adenocarcinoma or non–small-cell lung cancer induces rare PR or no remissions (NSCLC), but it is being re-tested in combination with standard chemotherapy. With gemcitabine, R115777 induced myelosuppression and other toxicities in 30 patients with advanced solid tumors, but 8 PR were recorded. The PR rate in patients with metastatic breast cancer was 14%. Intermittent administration (ID) of tipifarnib was better tolerated than the continuously administered (CD) drug and tipifarnib showed weak activity against advanced breast cancer: 10% PR and 15% stabilization of disease occurred in the CD cohort, and 14% PR and 9% strabilization of disease occurred in the ID cohort [177–186]. Patients with AML or with advanced breast cancer are being recruited for clinical trials with R11577 (http://www.centerwatch.com/trials/). The summary from the literature of NSCLC treatment data shows the peformance of tipifarnib (with docetaxel and/ or gemcitabine) to be 1 CR and 5 PR in 20 patients, and lonafarnib (with paclitaxel) to be 12 PR in 45 patients and 14 minor response (MR) or stabilization of disease (SD) in 33 patients. These are weak agents; viral therapy could match or surpass their efficacy [187]. L778123 (Eli Lilly, Indianapolis, IN; Merck, Whitehouse Station, NJ) is a peptidomimetic FT inhibitor active on CAAX. It is a dual inhibitor of FT and geranylgeranyl protein transferase (GGPT) [188–190]. It caused thrombocytopenia and partial heart block (prolonged QT), but it induced CR in some exceptional patients with NSCLC and head and neck carcinomas, especially when given in combination with radiotherapy. Farnesyl transferase inhibitors now in clinical trials (R11577, BMS-214662, BMS-186511, L-774123, L-778123, SCH44342, PD083176, PD98059) have been repeatedly reviewed [187,191]. Extracellular signal-regulated kinases are overactive in AML cells but can be inhibited by PD98059 (New England BioLabs, Beverly, NJ); downmodulation of ERK resulted in cell-cycle arrest and apotosis of the leukemic cells [190].


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Rho GTPses bind GTP and hydrolyze it to GDT. Rho GTPaseactivating proteins (Rho-GAPs) organize eukaryotic cytoskeleton and gene transcription. Cells of inflammatory carcinoma of the breast overexpress RhoC GTPase and treatment with L774123 or L774832 suppressed the expression of this enzyme and the malignant phenotype (decrease of anchorage-independent growth; locomotion and invasiveness) of these cells [193]. In summary, FT inhibitors (R115777, BMS214662, L778,123) used singly in patients with metastatic disease induced only occasional PR or MR, but more frequently caused stabilization of disease. In patients with pancreatic or lung cancers, there were no real responders; in metastatic breast carcinoma, 10% PR and 16% stabilization of disease occurred; occasional PR are recorded in patients with recurrent glioma, AML, or myelodysplasia. In combination with gemcitabine, paclitaxel, or platinols, or with radiotherapy, the PR rate rises and occasional CR are also recorded, with a trend suggestive of additive effects. Ras antagonists transfarnesylthiosalicylic acid (FTS) or SCH66336 block the growth of human melanoma xenografts in SCID mice [166,194]. Ras-transformed tumor cells do not express Fas (CD95) and therefore escape externally induced apoptosis. Farnsyl transferase inhibitor LB42722 upregulates Fas (CD95) expression and restores susceptibility of the cell to apoptosis; the same compound inhibits VEGF expression [195]. N-ras–transformed neuroblastoma cells utilize insulinlike growth factor (IGF)-II, nerve growth factor (NGF) and brain-derived neurotrophic factor in their autocrine growth loops. The FT inhibitor FTI-277 disrupts these autocrine growth loops [196]. The peptidomimetic FT inhibitors B956 and B1086 suppress colony formation in soft agar, or growth in xenografts of human fibrosarcoma, urinary bladder carcinoma, and colon carcinoma cells [197]. The enzyme nucleoside diphosphate kinase (Ndk) attacks the mutated Ras protein RasD12, but not the wild-type Ras protein; it may act in vivo as a metastasis suppressor [198]. The small molecular compound HA14-1 binds and inhibits Bcl-2 and increases cytochrome C release from mitochondria. These are pro-apoptotic events. The isoquinolone carboxamide derivative PK11195 is an an-

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tagonist of the mitochondrial benzodiazepine receptor (PBR) and thereby reinforces HA14-1-induced apoptosis, whereas Ro-4864, an agonist of PBR, protects tumor cells against TNF␣-induced apoptosis [199]. The HA14-1 and PK11195 combination is awaiting clinical trials. PK11195 eliminates BclXLⳭ and Mcl-1Ⳮ cholangiocarcinoma xenografts [200]. PK11195 sensitizes AML cells to daunomycin and cytarabine [201]. The lactone of Aspergillus terreus, lovastatin, depletes intracellular mevalonates and synergizes with interferon (IFN-␣2b) in suppressing the growth of, and inducing apoptosis in, the CML cell line K562 [202]. SU11248 [Sugen (now Pfizer, New York, NY)] inhibits PDGF-R, VEGF-R, c-KIT (cyclin-dependent kinase inhibitor tumor), and FLT3 (the fmslike tyrosine kinase) and suppresses the growth of M.D. Anderson Hospital breast cancer xenografts [203]. The PI3K inhibitor LY294002 restores cancer cells’ susceptibility to ionizing radiation. LY294002 renders pancreatic cancer cells susceptible to sulindac. LY294002 and the mTOR inhibitor rapamycin induce the expression of cycline kinase inhibitor p21 in prostate cancer cells but BclXL protects prostate cancer cells against LY294002-induced apoptosis (204–207). Tyrphostin AG490, the JAK inhibitor in pancreatic carcinoma cells, downregulated cyclin D1, BclXL, and VEGF mRNA. In anaplastic lymphoma cells, it induced expression of the proapoptotic caspase 3 and suppressed Bcl-2 and BCLXL. Tyrphostins arrest the cell cycle in ovarian carcinoma cells [208–210]. These tumors are targeted for reoviral therapy: There appears to be a rationale for a combined attack on these tumor cells. TYROSINE KINASE INHIBITORS Imatinib Mesylate The reciprocal translocation t(9;22)(q34;q11) linking the gene c-abl to the 5′ segment of gene bcr forms the fusion gene bcrabl. The p210bcr-abl oncoprotein product of the fused gene functions as a tyrosine kinase in PhⳭ CML cells. It is recognized by CD4 and CD8 T cells of the host. The implications of graft-vs


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leukemia reaction and immunotherapy directed against this target have been explored [211,212]. The phenylamino pyrimidine STI-571 (imatinib mesylate, Gleevec, Novartis) emerges as the most efficient inhibitor of the phosphorylated gene product protein. It induces 94% CR in CML with 91% cytogenetic response; freedom from progression and survival at 18 months are 93% and 96%. This drug is now fully licensed for the primary treatment of CML, even in the accelerated or blast crisis stages of the disease. In the accelerated phase of CML, complete cytogenetic response rate is 24%, extending 18-month survival up to 73% [213–223]. Imatinib may control hypereosinophilic syndromes with or without the translocation t(5; 12)(q33;p13) [222]. The FT inhibitors SCH66336 or R115777 are additive to imatinib in suppressing PhⳭ CML cells [225,226]. The pyrido-pyrimidine compounds PD166326, PD173955, and PD180970 inhibit both abl and src kinases and suppress the growth of imatinib-resistant CML cells [227,228]. CML K562 xenografts regress in nude mice treated with the perorally administered anilino-quinoline-carbonitrile SKI-606 (Wyeth), a dual inhibitor of src and abl tyrosine kinases [229,230]. A 10-fold increase in the BCR-ABL fusion transcript (caused by mutations in the bcr-abl genes) is the cause of imatinib resistance [231,232]. When imatinib destroyed mast cells in the tumor bed of human mammary carcinoma xenografts, accelerated growth of the tumors occurred [233]. This compound may be active in the treatment of systemic mastocytosis. However, in an actual assay, STI571 failed to inhibit the growth of human leukemic mast cell lines [234]. The Hardy-Zuckerman (HZ4) feline sarcoma retrovirus harbors the oncogene v-kit, which derives from the host cell gene c-kit. It serves as the receptor (CD117) for its cognate ligand stem cell factor (SCF). When phosphorylated on Tyr567 and Tyr 719, the gene product protein of this gene induces the JAK/STAT (Janus family kinases/signal transducers and activators of transcription), the Ras-Raf protein kinases, the PI3K, the MAPK, and the PCL (phosphokinase C) systems, leading to mitoses and apoptosis-free survival of the cell. If the signal transduction emanates from a point-mutated c-kit (exons 9,

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11, or 13), the system remains constitutively activated and the cell exhibits all criteria of the malignant geno- phenotype, especially those of invasiveness and neoangiogenesis induction. STAT3 is constitutively activated, but JAK2 can be blocked with AG490 (Tyrphostin); MAPK are blocked by PD98059; PI3K is blocked by LY294002, but only STI571 (imatinib) or AG490 could inhibit proliferation of malignant gastrointestinal stromal tumor (GIST) cells [235–245]. Malignant cells expressing the receptor c-kit and its ligand SCF utilize the system as an autocrine growth loop. Prominently expressed in the notoriously chemotherapy-resistant GIST, c-kit signal transduction is inhibited by imatinib mesylate. However, c-kit is frequently mutated and constitutively activated without capturing its ligand. Occasionally, not c-kit but the PDGF-R gene is mutated. When imatinib mesylate inhibits c-kit signal transduction, the cell becomes susceptible to programmed death; when Bcl-2 is amplified (not translocated), GIST cells become apoptosis-resistant. Gastrointestinal stromal tumor cells are usually positive for vimentin and CD34 and could express a-smooth muscle actin and S-100. Bcl-2, c-Myc, and Ki-67 overexpression correlates with a highly malignant course. Prognosis worsens with tumors being aneuploid [237] and harboring a mutated p16INK4 gene at 9p21 [239]. This c-kit suppressor gene is frequently mutated in a number of human malignant tumors. Imatinib induces up to 40% PR rates in metastatic disease and is now fully licensed for the treatment of GIST [240]. Dosage exceeding 500 mg/ day induces toxicities (edema, nausea, diarrhea, myalgia, skin rash, myelosuppression with bleeding). Overexpressed and/or mutated c-kit is operational in colorectal adenocarcinomas or in glioblastoma cells; cultured or xenografted cells of these and other (small-cell undifferentiated carcinoma of the lung) tumors are also inhibited by imatinib mesylate [246,247]. In small-cell carcinoma of the lung (SCLC), the tumor cells use c-kit and its ligand SCF in autocrine and paracrine growth loops [248,249]. Anaplastic thyroid carcinoma cells also expressing CXCR4, the chemokine receptor for stromal cell-derived factor-1␣ (SDF-1␣), continue to proliferate in the presence of imatinib; the PI3K-inhibitor LY294002 inacti-


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vated these cells [250], calling for clinical trials in which imatinib and LY294002 are combined. Imatinib potentiated the efficacy of cis-platin against lung cancer cells and clinical trials of carboplatin with paclitaxel plus imatinib are being initiated. Recently, c-kit expression was detected in choroidal melanoma cells [251]. Pediatric sarcoma, synovial sarcoma, osteosarcoma, and Ewing sarcoma cells are frequently positive for c-kit [236,252]. Nonmutated c-kit is overexpressed in the majority of postradiation sarcomas [253], which are usually chemotherapy-resistant and are awaiting clinical trials with imatinib. Some sarcomas (osteosarcoma, dermatofibrosarcoma protuberans, and others) utilize platelet-derived growth factor and its receptor (PDGF;R) and its ligand as an autocrine growth loop. Nonmesenchymal tumors with an operational PDGF→R system include melanoma, neuroendocrine carcinoids and carcinomas, and many adenocarcinomas. Imatinib mesylate suppressed PDGF-R signaling in cultured and xenografted human osteosarcoma cells and induced remissions in patients with DFSP. In this latter tumor, the PDGF gene (encoding for the ligand) undergoes translocation t(17;22)(q22; q13), in which the collagen type 1 promoter gene drives the PDGF ␤-chain gene, resulting in an autocrine growth circuit. The retrovirally transduced counterpart of this gene v-sis (csis: 22q12.3-12.1 in the human genome) was discovered in the simian sarcoma retrovirus. The gene c-sis is active in wound healing, atheroscleotic plaques, first trimester cytotrophoblasts, transformed fibroblasts, Kaposi’s sarcoma cells, other sarcomas, and in several carcinomas, especially in desmoplastic reactions induced by neuroendocrine tumors, certain melanomas, and breast carcinomas. Imatinib mesylate induces dramatic remissions in cases of DFSP by suppressing signal transduction from PDGF-R (failures of treatment are also on record) [254–257]. Expectations have been raised as to the treatment of myelofibrosis, desmoid tumors, and some sarcomas with imatinib mesylate. New phenylamino-methyl-pyrido-pyrimidine compounds (PD173955; PD166326; PD180970) unrelated to, but potentially cooperative with, imatinib emerge as most potent inhibitors of the Bcr-Abl oncoprotein autophosphorylation. The src

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kinase (the Rous sarcoma virus oncogene) inhibitor PD180970 suppressed the growth of CML blast crisis-derived leukemic cells (K562). Mutated Abl kinase (threonine for methionine at amino acid 351—M351T) gains resistance to imatinib mesylate, but remains susceptible to PD180970; this compound also inhibits signal transduction from nonmutated (wild-type) c-kit [258–261]. Bcr-AblⳭ CML cells exhibit increased susceptibility to STI571 combined with histone deacetylase inhibitors [aphicidin, depsipeptide, soberoylanilide hydroxamide acid (SAHA), sodium butyrate, oxamflatin, trichostatin, FR901228, MS-275]; SAHA in itself could induce either differentiation or apoptosis of leukemic or solid tumor (pancreatic, small-cell undifferentiated lung carcinoma) cells [262–268]. Raf inhibitor L-779,450 and PI3K inhibitor LY294002 act additively against leukemic cells [269]. HT29 human colon carcinoma cells overexpress c-kit and respond to SCF, while remaining susceptible to inhibition by PI3K antagonist LY294002, to Rho GTPases (Clostridium botulinum exoenzyme transferase), and to inhibitors of Rho kinases (L27632, STI571, Y27632) [270]. The ROCK (Rho-associated kinase) inhibitor Y-27632 and C. botulinum C3 exoenzyme inhibit lysophosphatic acid expression in ovarian carcinoma cells that is essential for tumor cell migration [271]. SU11248 (Sugen) inhibits signal transduction from both EGF-R and PDGF-R and is being tested in patients with SCLC. EGF-R and HER2/neu may form homo- or heterodimers. SU11248 inhibits c-kit and PDGF-R␤ in SCLC; GW2016 inhibits both EGF and Erb2 tyrosine kinases [272–274]. The fms-like tyrosine kinases (FLT) and their ligands drive hematopoietic cell maturation from their loci at chromosomes 5q31 and 13q12. The gene was discovered in the McDonough feline sarcoma retrovirus (v-fms); c-fms encodes the receptor for M-CSF. This receptor family includes stem (steel) factor receptor Kit and platelet-derived growth factor receptors A and B (PDGF-R). When c-fms undergoes internal tandem duplication (ITD) mutation, it contributes to the generation of AML cells. Tyrosine kinase inhibitors (TKI) aimed at FLT include indolo-carbazoles and the herbimycins and geldanamycins, which inhibit heat shock protein 90, the chaperone


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that protects oncoproteins from degradation in proteasomes. Sugen product SU5416, quinazolines (MLN518), and staurosporine derivatives (PKC412) inhibit FLT signaling pathways. Patients with AML receiving treatment with one of these TKI may achieve PR. The preparations GTP14564 and SU11248 also inhibit FLT3 [275–277]. SU6656 (Sugen) and/or PD180970 inhibit src-kinase and the STAT pathway in lung cancer cells, eliciting apoptosis. Antisense STAT3 oligonucleotides or adenoviral vector expressing dominant negative STAT3 isoforms also induced tumor cell death [278]. CP-65477 is a selective Erb2 kinase inhibitor in breast cancer cells [279]. The monoclonal antibody 2C4 also targets Erb2 because it is expressed in breast and prostate cancer cells [280]. The growth of a renal cancer cell line is stimulated by EGF and TGF␣; the EGF-R tyrosine kinase inhibitor PK11166 and paclitaxel cooperate in apoptosis induction of tumor xenografts and endothelial cells supporting the tumor [281]. The isoquinoline ligand of the mitochondrial benzodiazepine receptor ihibitor PK11195 counteracts multiple drug resistance of some leukemic and ovarian carcinoma cells [282]. Epstein-Barr virus carrier malignant lymphomas utilize IL-6 and IL-10 in their autocrine growth loops. The microbial macrolide (macrocyclic lactone) rapamycin (sirolimus; Rapamune, Wyeth-Ayerst Laboratories, St. Davids, PA) is immunosuppressive, arrests cells in G1, and kills lymphocytes, so it emerges as a therapeutic modality for those lymphomas, which appear in organ transplant recipients. Its analogues CC1-779 (Wyeth-Ayerst) and RAD001 (everolimus; Novartis) act upon the serine-threonine kinase receptor mTOR, which bears homology with PI3K. Combining rapamycin with LY294002 increased its growth-inhibitory effect on prostate cancer cells because PI3K, AKT, and mTOR signaling drives the growth of prostatic cancers. The growth of osteo- and rhabdomyosarcoma cells; medulloblastoma, neuroblastoma, and glioblastoma cells; lung cancer cells (SCLC); and some adenocarcinoma (breast and prostate) cells was inhibited by rapamycin [283–292]. ZD1839 Gefitinib Epidermal growth factor receptor is commonly constitutively overexpressed in human cancer cells and it is targeted by in-

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hibitors of its tyrosine kinase and by monoclonal antibodies [293–301]. The anilino-quinazoline derivative ZD1839 (Iressa, AstraZeneca) selectively and reversibly blocks the EGF-R tyrosine kinases. The EGF-R/ErbB1 (7p11-13 in the human genome) and its family (HER2, 3, 4 for human epidermal receptor) with their ligands, heregulin for HER3 and neuregulin for HER4, are proto-oncogenes whose ancestors were discovered in the genome of the avian erythroblastosis retroviruses as verb2, 3, 4. EGF-R captures EGF, transforming growth factor alpha (TGF␣), amphiregulin, and heparin-binding growth factor as its ligands. Truncated EGF-RvIII without its extracellular domain is constitutively active in glioblastoma and in some breast carcinoma cells. However, in some human tumor cell lines (breast cancer, lung cancer) ZD1839 acted independently from EGF-R expression [302,303]. ZD1839 in low dose suppressed the growth of cultured or xenografted human carcinoma cells; in high dose it induced apoptotic deaths. In treated tumor cells, the cell cycle stops at G1 and the p27 cyclinedependent kinase inhibitor levels rise. Apoptosis induction is enhanced by platinols or radiation. In xenografted tumors, VEGF, bFGF (vide infra), and TGF␣ levels drop: Iressa exerts anti-angiogenesis. Signal transduction in breast carcinoma cells from the HER2/neu/ErbB2 receptor is also suppressed; this effect is intensified by the co-administration of trastuzumab (Herceptin, Genentech). The growth rate of xenografted ovarian carcinoma cells was significantly retarded by ZD1839 in SCID mice. When tested against xenografted prostate carcinoma cells, Iressa synergized with bicalutamide [304–306]. In an AstraZeneca trial (reported by R.S. Herbst from M.D. Anderson Cancer Center, Houston, TX) of 71 patients with NSCLC, only one experienced PR, but in most of the patients, the disease stabilized for 3 (45%) to 12 months (7%) [307,308]. In Phase II clinical (IDEAL—Iressa dose evaluation in advanced lung cancer) trials, chemotherapy (taxanes and platinols)-resistant NSCLC appeared to be sensitive to Iressa monotherapy: The orally administered drug induced 8% to 18% durable PR rates; with stabilization of disease, the response rate rose to 53%, but 34% of patients progressed after


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a stagnation of tumor growth for 4 months. When combined with carboplatin or paclitaxel for 24 untreated patients, one CR, five PR, and eight stabilizations of disease occurred. Clinical trials of Iressa in combination with 5FU or gemcitabine with or without platinols or taxanes continue. Tolerated dosage is 250 to 500 mg/day. Higher dosages cause diarrhea and acneiform skin eruptions. The Phase III (INTACT) clinical trials failed to prove improved survival rates when Iressa was added to chemotherapy for the treatment of NSCLC because the control group in this trial achieved an unexpectedly high survival rate. The addition of gefitinib to the standard paclitaxel and carboplatin regimen in the treatment of advanced NSCLC did not prolong survival (INTACT 2 trial). There is good agreement among clinical trials on Iressa’s tolerable toxicity profile and on its efficacy in inducing responses (PR; stabilization of disease) even in chemotherapy-refractory patients [309–317]. According to case reports, bronchioalveolar carcinoma appears to respond better to Iressa than other histological types of lung cancer [318,319] due to EGF-R mutations. In pre- or early clinical studies, Iressa suppressed the growth of some selected solid tumors (colorectal adenocarcinoma, squamous cell carcinoma of the head and neck) and synergized with radiotherapy (oral squamous cell carcinoma) and chemotherapy (5FU, capecitabine, and the platinols) [320–330]. In Japan, tens of thousands of patients received Iressa but 80 cases of interstitial pneumonitis, sometimes advancing into fatal pulmonary fibrosis, emerged [331]. Bronchial alveolar cell damage [332] might have occurred prior to pulmonary fibrosis. The Oncologic Drug Advisory Committee (ODAC) approved the licensure of Iressa [333] for the treatment of patients with NSCLC who failed chemotherapy with platinols and taxanes. OSI-774 Erlotinib The quinazoline-derivative CP-358,774 or OSI-774 (erlotinib, Tarceva, OSI Pharmaceuticals; Genentech) inhibits EGF-R tyrosine kinases. The drug gained fame when it induced CR in

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a patient with metastatic kidney carcinoma (whose primary tumor was then resected) for more than 20 months. Other patients with a variety of metastatic carcinomas experienced PR (11% to 13%) and long stabilizations of disease (34% to 58%). Of bronchogenic carcinomas, bronchioalveolar carcinoma appears to respond best to erlotinib (ASCO 噛2491 2003). Some of these patients developed severe but reversible papulopustular acneiform skin eruptions. Both Iressa and OSI-774 act on the normal epidermis of cancer patients in upregulating cell-cycle inhibitor p27 and decreasing autophosphorylation of the EGFR on Tyr1173. Of 34 patients with ovarian carcinoma, 3 PR and 15 stabilization of disease occurred. Clinical trials with erlotinib and docetaxel for advanced NSCLC are not without side effects: Febrile neutropenia, diarrhea, stomatitis, and acneiform skin rash occur, and the maximum tolerated dosages (100 mg/day and 75 mg/m2 every 3 weeks) are not to be exceeded. [334–337]. PART I: RECENT DEVELOPMENTS IN VIRAL ONCOLYSIS The Chinese HOT vaccine consists of a recombinant oncolytic adenovirus (Ad-sp/E1A) expressing heat shock protein (HSP70); HSP-complexed antigenic peptides from tumors, when presented to DCs, elicit rejection-strength immune reactions of the host [338]. Viral vectors (AdCMVIl-12) injected intratumorally may disseminate in the host [339]. The histone deacetylase inhibitor depsipeptide (FR901228; FK228, NCI, Bethesda, MD) is in Phase II clinical trial; it enhances adenoviral receptor CAR expression and thereby promotes adenovirally inserted transgene expression in targeted cells [340]. The efficiency of adenoviral gene transfer depends on the extent of CAR expression in NSCLC xenografts [341]. The current status of gene therapy for lung and head and neck cancers is dominated by adenovirally inserted wildtype p53 gene into tumor cells [342]. Although success rate is limited, adenovirally inserted wild-type p53 increases the radiosensitivity and decreases the DNA repair capacity of


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the tumor cells [343]. The R1 subunit of the enzyme ribonucleotide reductase (RNR) acts as a tumor suppressor; intratumorally injected rAd5-R1 inhibits the growth of human colon carcinoma xenografts [344]. Both Ras and the adenovirally produced small VA (virus-associated) RNA block PKR; otherwise, adenovirally produced dsRNA would activate PKR, viral protein translation would be blocked, and IFN would abolish viral replication, as it does in healthy cells. In Rasmutated tumor cells, adenoviral infection does not depend on its VA small RNAs; there PKR is already blocked. Therefore, VA gene-defective adenovirus could not replicate in normal cells but would selectively grow in Ras-mutated tumor cells. The dl330 (29 bp-deleted VAI RNA-coding region) Ad5 VAI mutant is therefore a new candidate for virotherapy of Ras-mutated cancers [345]. Human cancer cells often overexpress MMAC (mutated in multiple advanced cancers) and PI3K/Akt and eliminate the tumor-suppressor gene PTEN (phosphatase and tensin homologue deleted on chromosome ten). The ‘‘kinase dead mutant of Akt’’ replicationdefective Ad-Akt-DN E1/E3-deleted adenoviral vector selectively induces apoptosis in tumor cells [346]. In kidney carcinoma cells with mutated von Hippel-Lindau (VHL) gene, the hypoxia-inducible factor (HIF) is overexpressed and escapes proteasomal degradation because of faulty ubiquination. The replication of adenovirus construct Ad9xHRE1A is HIF-dependent and, therefore, it selectively kills VHL gene-mutated tumor cells (pheochromocytoma, renal cell carcinoma) [347]. A replication-competent adenovirus contains two cell suicide genes fused: those of cytosine deaminase (CD) and herpes simplex virus (HSV) tk. Prostate cancer cells infected with AD5-CD/TKrep cannot rapidly eliminate 5-fluorocytosine and die upon exposure to valganciclovir; these tumor cells show increased sensitivity to radiation therapy [348]. Genetically engineered adenoviruses facilitate pro-drug therapy by sensitizing tumor cells (hepatocellular carcinoma, human tumor xenograft 293/E4, breast carcinoma) to gemcitabine, irinotecan, or mitomycin C 349–351 (Table 1). Vaccinia and canarypox (ALVAC, Aventis Pasteur, Swiftwater, PA) viruses delivering genes for HPV16, HPV18E6, and HPV18E7; GM-CSF; or

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338. Huang XF, Ren W, Rollins L, Pittman P, Shah M, Shen L, Gu Q, Strube R, Hu F, Chen S-Y. A broadly applicable, personalized heat shock protein-mediated oncolytic tumor vaccine Cancer Res 2003; 63:7321–7329. 339. Wang Y, Hu JK, Krol A, Li Y-P, Li C-Y, Yuan F. Systemic dissemination of viral vectors during intratumoral injection Molec Cancer Therap 2003; 2:1233–1242. 340. Goldsmith ME, Kitazonoi M, Fok P, Aikou T, Bates S, Fojo T. The histone deacetylase inhibitor FK228 preferentially enhances adenovirus transgene expression in malignant cells Clin Cancer Res 2003; 9:5394–5401. 341. Qin M, Chen S, Yu T, Escuardo B, Sharma S, Batra RK. Coxsackievirus adenovirus receptor expression predicts the efficiency of adenoviral gene transfer into non-small cell lung cancer xenografts Clin Cancer Res 2003; 9:4992–4999. 342. Moon C, Oh Y, Roth JA. Current status of gene therapy for lung cancer and head and neck cancer Clin Cancer Res 2003; 9:5055–5067. 343. Sah NK, Munshi A, Nishikawa T, Mukhopadhyay T, Roth JA, Meyn RE. Adenovirus-mediated wild-type p53 radiosensitizes human tumor cells by suppressing DNA repair capacity Molec Cancer Therap 2003; 2:1223–1231. 344. Cao M-Y, Lee Y, Feng N-P, Xiong K, Jin H, Wang M, Vassilakos A, Viau S, Wright JA, Young AH. Adenovirus-mediated ribonucleotide reductase R1 gene therapy of human colon adenocarcinoma Clin Cancer Res 2003; 9:4553–4561. 345. Cascallo M, Capella´ G, Mazo A, Alemany R. Ras-dependent oncolysis with an adenovirus VAI mutant Cncer Res 2003; 63: 5544–5550. 346. Jetzt A, Howe JA, Horn MT, Maxwell E, Yin Z, Johnson D, Kumar CC. Adenoviral-mediated expression of a kinase-dead mutant of Akt induces apoptosis selectively in tumor cells and suppresses tumor growth in mice Cancer Res 2003; 63: 6697–6706. 347. Cuevas Y, Hernańdez-Aloceba R, Aragones J, Naranjo-Sua´rez S, Castellanos MC, Estaban MA, Martin-Puig S, Landazuri MO, del Peso L. Specific oncolytic effect of a new hypoxia-

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PART II: FLAVOPIRIDOLS, PROTEIN KINASE C, METALLOPROTEINASES, AND CYCLOOXYGENASE INHIBITORS FLAVOPIRIDOLS Cyclins Cycline-dependent kinases (CDK) in their complexes with cyclins and their inhibitors (p15, 16, 21, 27, and especially p16INK4) regulate the cell cycle [1]. CDK2, 4, and 6, in combination with cyclins E and D, promote progression of the cell cycle from G to S; CDK2 and cyclin A and CDK1 and cyclin B carry the cell through the S phase to conclude mitosis. When the cycline kinase inhibitors (CKI) suffer mutation, the cell cycle progresses through mitoses incessantly—non-stop. Flavonoids occur naturally and can be isolated from the stem bark of the Indian plant Dysoxylum binectariferum. Flavopiridols (FP) (flavopiridol, L868275, Aventis), including olomoucin-roscovitine (R-roscovitine, CYC202, Cyclacel, Dundee, UK), the semisynthetic flavonoids, imitate the activity of, and can serve as replacement for, mutated CKI; they also inhibit EGF-R kinases and PKC. Some leukemic cells, when their mutated CKI is replaced by FP, activate the mitochondrial apoptotic death cascade. Flavopiridols, roscovitine, and the PI3K inhibitor LY294002, together, acted most efficiently against the PI3K/Akt, Bcl-2, and Mcl-1 pathways. PI3K phosphorylates membrane phosphatidyl inositol, thereby creating polyphosphoinositides. The lipid phosphatase gene product protein MMAC/PTEN (mutated in cultiple advanced cancers/phosphatase on chromosome ten; myotubularin; phosphatase and tensin homolog deleted on chromosome ten) [2] dephosphorylates polyphosphoinositides, but MMAC/PTEN is often mutated or deleted in human cancers. Wortmannin, LY294002, and PD98059 could inhibit PI3K-Akt cell survival pathway and thereby induce apoptosis in cancer (pancreatic and ovarian

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carcinoma) cells. Flavopiridols synergize with TRAIL, the TNF-related apoptosis-inducing ligand, and inhibit NF-␬Bdependent gene transcription, so TNF␣ is not antagonized in FP-treated cells [3]. Flavopiridols are forceful inducers of IL-6 [4]. Substratum-attached cancer cells operate with an upregulated PI3K-Akt pathway but LY294002 could induce apoptosis in these cells [5] (see Part I of this chapter). The genomic sequence v-akt was discovered in the directly transforming AKR murine retrovirus AKT8 isolated from thymic lymphomas of the mouse; v-akt is the derivative of the cellular genomic sequence c-akt, which was transduced by the retrovirus. The human AKT2 protein is a serine-threonine kinase with src homology and it is activated by PI3K, PDGF, bFGF, EGF, and IGF. The PI3K inhibitor LY294002 kills acute myeloblastic leukemia cells by inducing apoptosis. Flavopiridol inhibitors (see Part I) activate Rho-B proteins, regulators of cytoskeletal actin organization and cell adhesion; the geranylgeranylated Rho-B-GG proteins mediate arrest of the cell cycle and promote apoptosis, especially when a combination of FT and PI3K-Akt inhibitors is applied. RhoGD12 has been recognized as a metastasis-suppressor protein [6]. In vitro and xenograft assays show that FP induce apoptotic death of SCLC cells [7], potentiate the effect of STI571 in BCR-ABLⳭ CML cells [8–12] and that of docetaxel in pancreatic and gastric cancer cells [13], enhances EGF-R suppression by trastuzumab in breast cancer cells [14], and increases radiosensitivity of ovarian cancer cells [15,16]. However, in a clinical trial, FPs were ineffective against advanced colorectal cancers [17]. Adenovirus ONYX certainly promises a better performance in this tumor category (see Part I). Flavopiridols synergize with the histone deacetylase (HDAC) inhibitor Na-butyrate and intensify apoptosis induction in human leukemia cells [18], in which they reduced Rb protein/E2F1 complex formation, downregulated Mcl-1, and induced caspase-mediated cleavage of Bcl-2. Histone deacetylase 5 is an early p53 transcript; in HDAC 5-transfected hosts, osteosarcoma, neuroblastoma, and breast carcinoma cell growth is suppressed through the TNF␣-to-its-receptor pathway. Histone deacetylase 1, 2, and 3 deacetylate p53 (an anti-


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apoptotic event), whereas they stabilize p53 (a pro-apoptotic event). In pancreatic adenocarcinoma cells, HDAC-mediated downregulation of TGF␤R occurs; TGF␤ is inhibitory to epithelial cell growth and its inhibitory effect on pancreatic carcinoma cells is thus annulled. Histone deacetylase inhibitors (depsipeptide, trichostatin) cause cell cycle arrest by inducing the wild-type p53-activated protein p21WAF1 and dephosphorylation of Rb. In imatinib-resistant CML K562 cells, the addition of HDAC inhibitors [suberoylanilide hydroxamide acid (SAHA)] synergistically induced apoptosis. The benzamid derivative MS-275 (Nihon Schering KK, Chiba, Japan) is a HDAC inhibitor and inducer of mitochondrial cytochrome C-mediated apoptosis of human leukemia cells. Of the HDAC inhibitors (aphicidin, Na-butyrate, oxamflatin, SAHA, trichostatin A, and FR901228), a depsipeptide from Chromobacteriun violaceum upregulates the coxsackievirus and adenovirus receptors CAR and ␣␯ integrins on the surface of cancer cells thus rendering these cells susceptible to adenoviral infection; this compound offers itself to cooperate with oncolytic adenoviruses. The E1, E3 gene-depleted replication-defective type 5 Ad5.CMV-LacZ adenovirus (Qbiogene, Carlsbad, CA) could enter FR901228-pretreated cells. FR901228 exerts strong antiproliferative effect on lung cancer cells; in multidrug-resistant (MDR) SCLC, it inhibited telomerase mRNA; cycloheximide antagonized this effect. Depsipeptide failed, but SAHA or oxamflatin could kill P-glycoprotein-positive MDR malignant (T cell leukemia, colon carcinoma) cells (see Part I). Flavopiridol-Induced Apoptosis Flavopiridols induce apoptosis in B-CLL and multiple myeloma cells through reducing the expression of anti-apoptotic proteins Bcl-2, BclXL, and Mcl-1. Overexpression of Mcl-1 protects multiple myeloma cells against apoptosis; FP target Mcl1 (vide infra). In human breast carcinoma cells, FPs downregulate the apoptosis-inhibitory protein (IAP), BclXL, Mcl-1, and survivin. Flavopiridols synergize with the tubulin-polymerizing agent epothilone [19]. Epothilones are naturally occurring

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macrolides that polymerize tubulins, cause cell-cycle arrest at G2-M, and therefore elicit apoptosis even in cancer cells resistant to taxanes; they may be synergizing also with gemcitabine, capecitabine, or with the platinols when tested in patients with pancreatic cancer. A preliminary report indicates that patients with visceral metastases of breast carcinoma responded to epothilone (BMS-247550, Bristol-Myers Squibb) with PR and stabilization of disese (ASCO 噛30 2003). Cells protect themselves against TNF-induced apoptosis by activation of NF␬B. In human tumor cells, FPs synergize with TNF␣. Flavopiridols inhibit NF␬B and overcome apoptosis resistance [3]. In colon carcinoma xenografts, FPs synergized with CPT11 (irinotecan) [20]. STI571 (imatinib) and L86-8275 (FP) together were more effective in apoptosis induction in PhⳭ human leukemic cells than any of them alone [10]. Flavopiridols synergize with trastuzumab in breast cancer cells but breast cancer cells overexpressing both EGF-R and HER2/ neu(erb2) are resistant to this combination [14]. Inhibitors In melanoma cells, CDK1, CDK2, CDK4, and CDK6 act uninhibited; the Rb protein is phosphorylated because the suppressor protein p16 is not produced because of mutations in its gene; FP inhibits CDK in melanoma cells, which undergo apoptotic death [21]. Roscovitine ( Alexis Coger Co) is a radiosensitizer as tested against xenografted human breast or ovarian carcinoma cells [15,16]. The bioflavonoid quercetin (Sigma) sensitizes Ewing’s sarcoma cells to hyperthermia [22]. Quercetin suppresses proliferation of prostate cancer cells; in this latter case, signal transduction from Erb2, Erb3, and TGF␣ were mitosis-inducing for the tumor cells and quercetin antagonized this effect. The isoflavonoid genistein of soy products inhibits Akt after its phosphorylation by EGF-R kinases or by PI3K, therefore also blocking NF␬B activation. High-grade intra-epithelial prostatic hyperplasia in its peripheral zone may advance to invasive carcinoma, transgresses the capsule, and eventually metastasizes and gains hormone-refractory state. Overexpression of cyclo- and lipooxygenases because of


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arachidonic enzyme activities carries major responsibility for these changes. In cultured human prostate cancer cells, genistein induced apoptosis but left nontumorigenic prostate epithelial cells intact. The endogenous lipid anandamide downregulates EGF-R and exerts an antiproliferative effect in prostate cancer cells [23–26]. Survivin is a member of the IAP family; it is highly expressed in embryonic cells but is silent in differentiated adult cells. The anti-apoptotic survivin inhibits caspase 9 and is overexpressed in many human cancers. It can be inhibited by its antisense oligonucleotides (see Part III of this article) or by the nonphosphorylable T34A adenovirally delivered survivin gene (pAdT34A). When it reappears overexpressed in tumor cells, survivin is recognized by the tumor-bearing host, which mobilizes anti-survivin immune T cells (HLA-A24-restricted cytotoxic T cells); these cells expanded by IL-2 could be used for adoptive immunotherapy. Human leukocyte antigen-A24positive and survivin2B-positive cancer cells are killed by these immune T cells. Soft-tissue sarcomas frequently exhibit elevated survivin levels, predicting shortened life expectancy attributable to death with tumors. Mesothelioma cells thrive on the homozygous deletion of the INK4a/ARF locus: p14ARF is lost and the anti-p53 MDM2 protein is overactive in these tumor cells; in addition, 87% of mesotheliomas overexpress survivin. Anti-survivin oligonucleotides restored the susceptibility of mesothelioma cells to apoptosis. In gastric carcinoma cells, survivin mRNA expression is inversely correlated with the apoptotic index. Flavopiridols suppress survivin and inhibit its phosphorylation, depriving the tumor cell of its apoptosis-exempt status [27–36]. Flavopiridols synergize with taxanes and doxorubicin in inducing apoptosis in xenografted human breast cancer cells. In case of xenografted human colon carcinoma cells, FP synergized with the topoisomerase inhibitor CPT11 camptothecin (irinotecan). In bcr-abl–mutated MDR leukemic cells, FP synergized with STI571 (imatinib mesylate) and induced intrinsic (mitochondrial) apoptosis. Of 28 patients with mantle cell lymphoma, i.v. FP induced 3 (11%) PR and stabilized the disease in 20 (71%) patients. Intravenously infused FP in 55 patients

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with advanced neoplasms induced, in 12 cases, long stabilization of disease for 3 to 11 months (median 6 months). Flavopiridol-induced diarrhea is preventable with cholestyramine and lymphopenia is reversible [37–39]. If FP were administered to patients with oncolytic viruses, no possible antagonism between them can be foreseen. Would the attenuated measles virus synergize with FP in killing multiple myeloma cells? PROTEIN KINASE C INHIBITORS A Bad Kinase Protein kinase C (PKC) is a member of the serine-threonine kinase family. When induced by the diacylglycerol phorbol myristate ester, PKC contributes to the cell two criteria of the neoplastic phenotype: anti-apoptotic and pro-telomeric states. PKC␦, a member of the PKC family, is activated by IFN-␥ [40] and functions as an antagonist of ionizing radiation in breast carcinoma and glioblastoma cells [41,42]. Raf-1 (vide supra), which phophorylates Bcl-2, is a substrate of PKC. Protein kinase C activates telomerase reverse transcriptase (TeRT) and telomerase-associated protein (TeP-1) by phosphorylation, rejuvenating the cell. The Raf kinase inhibitor BAY 43-9006 performs well against colon carcinoma xenografts, especially when combined with irinotecan, vinorelbin, or gemcitabin [43]. Thromboxane (THX) A2 is captured by its receptors as expressed by glioma cells, leading to the activation of phospholipase C␤ and the activation of PKC. Phosphorylation of focal adhesion kinase (FAK) follows, leading to integrin activation and cell migration [44,45]. Thromboxane synthetase inhibitors arrest glioma cell migration and the immobilized cell may succumb to programmed death (see Part V of this chapter). Protein kinase C overexpressed in breast carcinoma and glioblastoma cells functions as a promoter of cell division. Protein kinase C expression in ovarian carcinoma reaches 52% of the tumors examined and represents an adverse prognostic factor [46]: This tumor awaits clinical trials with PKC inhibitors and is targeted for virotherapy (mumps, NDV, measles, and reovirus and genetically engineered HSV; discussed in this volume).


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Inhibitors Protein kinase C inhibitors are bryostatin (from the marine bryozoan Bugula maritima); the staurosprin derivatives OH, benzoyl UCN-01, and PKC-412; and ISIS3521, a phosphorothioate antisense oligodeoxynucleotide binding to PKC mRNA. Bryostatin suppresses PKC and upregulates TNF␣, IL-2, and 6, but induced only a few partial remissions (PR) in patients with solid tumors. In patients with metastatic kidney carcinoma, bryostatin induced remissions very seldom (6% PR), but durable (ⱖ 6 months) stabilization of disease occurred in 25% to 47% of patients. In 38 patients with advanced malignancies, prolonged infusions of bryostatin failed to induce remissions [47–50]. The hydroxystaurosporine UCN-01 and PKC412 synergize with 5FU by downregulating thymidylate synthetase in some adenocarcinomas (colon and cholangiocarcinomas). A preliminary report indicates that PKC412 inhibits a transmembrane tyrosine kinase active in AML and significantly reduces blast count in the blood (ASCO 噛2265 2003). UCN01 blocks the cell cycle at G1 and inhibited the growth of xenografted human squamous cell carcinomas of the head and neck, while stagnating tumor cells with suppressed CDK-2 activity died programmed cell death. Staurosporins downregulate XIAP (X-linked inhibitor of apoptosis). UCN-01 inhibits DNA repair in B-CLL and other tumor cells and offers itself as an adjuvant to cytotoxic chemotherapeutic drugs. ISIS3521 induced two CR in cases of non-Hodgkin’s lymphoma; it synergized with carboplatin in 53 patients with NSCLC, inducing 42% complete remission (CR), PR, and minor responses (MR), with median survival of 19 months. It suppressed rat gliosarcomas and breast carcinomas but failed to induce remission in the human counterparts of these tumors. Tamoxifen suppresses PKC in cultured human glioblastoma cells and synergizes with the nitrosourea BCNU. Accordingly, clinical trials are in progress with tamoxifen and cisplatin for pediatric brain tumors. The flavonoid quercetin inhibits PKC and suppresses the growth of ovarian carcinoma cells in vitro and in vivo it synergizes with cisplastin in xenografted human lung cancer

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cells; it inhibits the growth of human prostate cancer cells [51–57]. Neuropeptides (bombesin, bradykinin, vasopressin, neurotensin) are mitogenic for some (small-cell lung) cancer cells and tumor cells may make use of them through paracrine or autocrine growth loops. Neurotensin (NT) is a growth factor of certain K-ras– and c-raf–driven pancreatic cancer cells and exerts its effect through PKC activation. Protein kinase C inhibitors GF-1 (bisindolylmaleimide), U0126, and Ro 31-8220 (Calbiochem) counteracted NT [58,59]. METALLOPROTEINASE INHIBITORS Pathophysiology The endopeptidase matrix metalloproteinases (MMP)—collagenases, gelatinases, stromelysins, and matrilysins—promote tumor cell locomotion and invasion as they cleave laminin, hyaluronan, and cadherin. Some of the MMP, such as MMP9, the gelatinase that degrades type IV collagen, also cleave IL-2R of immune T cells or activate TGF␤ to inhibit expansion of immunoreactive T cell clones; or cleave CCL7, the monocyte chemoattractant protein-3 (MCP-3), thereby exerting tumorprotective functions [60–64]. Indeed, lung adenocarcinoma cells overexpressing MMP-9 are highly malignant [65]. CXCR-4 chemokine receptor captures its ligand CXCL12, the stromal cell-derived factor-1. This factor protects BCLL cells against apoptotic death and promotes metastatic spread of breast cancer cells. This factor is cleaved by MMP1, 3, 9, 13, and 14. When MMPs remove a tumor-protective factor, their blockade could promote tumor growth. Whereas most MMPs are expressed by stromal cells, MMP-7 (Matrilysin) is a product of epithelial cells such as certain adenocarcinoma cells; it promotes the growth of pancreatic carcinoma cells. Some murine mammary carcinoma cells co-express FasL and FasR, yet do not succumb to self-induced apoptosis except when exposed to MMP-7. In animals bearing this tumor, continuous treatment with MMP-7 selected out an apoptosisresistant cell population [66]. Insulinlike growth factor-l


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upregulates and IL-10 downregulates MMP-2 production in tumor cells [67]. Matrix metalloproteinase-2 production by lung and gastic cancers in China is associated with a single nucleotide polymorphism in the gene promoter of MMP-2 [68]. Phorbols (myristate acetate) induce MMP-9 but a fungal metabolite, dykellic acid, antagonizes this effect [69]. Bladder carcinoma cells overproduce MMP-9 and titrated high levels of MMP-9 in the urine indicate recurrence with invasive tumors [70]. These tumors are promoted by VEGF, bFBF, MMP-9, and IL-8 and are inhibited by IFNs, endostatin, angiostatin, and thrombospondin. Transfection of bladder cancer cells with the IL-8 gene increases, whereas IL-8 antisense sequences reduce, their malignant potentials; the ABX-IL-8 human anti–IL-8 monoclonal antibody downregulates MMP-9 production by, and inhibits the growth of, transitional carcinoma cells of the urinary bladder [71]. Prostate cancer cells produce membranetype MMP that cleaves laminin and thus promotes cancer cell migration [72]. Matrix metalloproteinase-19 is expressed in endothelial and vascular smooth muscle cells and is not associated with malignant transformation [73]. Some MPs can cleave TNF␣ or Fas ligand (L); adenoviral vectors of the FasL gene are available (RAdFasL) and induce tumor cell death, with release of sFasL from the apoptotic cells. The adenoviral vector RAdD4 encodes a noncleavable FasL that could not be antagonized by MMP [74]. FasL-expressing tumor cells kill FasRⳭ host immune T lymphocytes [75]; however FasLⳭ tumor cells are immunogenic in their hosts and induce rejection-strength immune reactions toward inocula of FasLⳮ autologous tumor cells. FasLⳭ tumor cells interact with the Fas receptor of DCs to elicit this reaction [76]. FasLⳭ tumors are infiltrated by polymorphonuclear leukocytes and suffer cell death but tumor cells can kill the leukocytes as well [77]. Some human melanoma cells have expropriated the FasL⇒Fas receptor system to function as an autocrine growth loop [78]. This is possible through the formation of a new putative fusion oncoprotein in which the extracellular domain is the Fas receptor and the intracellular domain is the G-CSF receptor: t(10; 1)(q23;p32). Capture of the FasL by this fusion oncoprotein would translate into mitogenic signal transduction [75]. Multi-

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ple–drug-resistant tumor cells overexpress the extracellular MMP inducer and MMP-1, 2, and 9 and thereby engage in accelerated invasiveness [79]. Reed-Sternberg (RS) cells express MMP-7, which activates MMP-2 in the stroma. Although RS cells are negative for MMP-9, T lineage lymphoma cells express it and the degree of expression correlates with advancement of the disease in the liver [80,81]. Inhibitors Trophoblasts and tumor cells degrade their extracellular matrix to promote their invasiveness. Of numerous inhibitors of MMPs (antisense oligonucleotides and ribozymes, anthrax toxin, peptidomimetic Batimastat and Marimastat, nonpeptidomimetic BAY12-9566, Prinomastat AG3340, tetracycline derivatives, Æ-941 Neovastat, bisphosphonates, acetylsalicylic acid), Marimastat prolonged life in certain subgroups of patients with pancreatic and gastric carcinomas; matrilysin promotes the growth of pancreatic carcinoma cells. When BAY12-9566 was compared with gemcitabine in patients with pancreatic carcinoma, it proved to be weaker than chemotherapy. Batimastat is effective against metastases of a rat mammary carcinoma only when treatment starts before removal of the primary tumor and is administered continuously thereafter. Its performance in human clinical trials is so far unsatisfactory [82–86]. Tabulated clinical trials of several MMPs show prolongation of life at the best [62]. Tetracycline derivative CMT-3 (Metastat) inhibitor of COX-2 and PGE2 (Hospitals of Joint Diseases, New York, NY) is being tested against Kaposi’s sarcoma and high-grade brain tumors. BAY12-9566 and ONO-4817 are called selective third generation MMP inhibitors (broad-spectrum first-generation: batimastat; secondgeneration: marimastat and prinomastat) [87]. The hydroxamate inhibitor prinomastat (AG3340) inhibited vitronectin proteolysis but did not antagonize the increased migration of human breast cancer cells, whereas inhibition of integrin degradation by MTI-MMP halted cancer cell motility [88]. ONO4817 (third-generation) inhibits the growth of human NSCLC


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(adeno- and squamous cell carcinoma lines) micrometastases in the lungs of nude mice and synergizes with chemotherapeuticals [89,90]. ONO-4817 inhibited regional lymph node metastases of an orthotopically xenografted squamous cell carcinoma cell line [89]. Testicans are heparin-chondroitin proteoglycans; N-Tes inhibits membrane-type matrix metalloproteinases (MT-MMPs) and testican-2 antagonizes this effect, therefore promoting invasiveness of glioma cells [91,92]. These weak agents do not compete with oncolytic viruses; the medical oncologist probably would favor the selection of an oncolytic virus for a clinical trial rather than one of the MMP inhibitors; it is unpredictable whether or not oncolytic viruses or MMP inhibitors would cooperate. CYCLOOXYGENASE INHIBITORS Eicosanoids Epidermal growth factor (EGF)-R and H-ras or K-ras overexpressions are essential for the maintenance of the malignant phenotype in colon adenocarcinoma cells. Signals emanating from EGF-R lead to phosphorylation of Extracellular regulated kinases (ERK)1, ERK2, and MAPK. Extracellular regulated kinases 1 and 2 and MAP kinases secure the anti-apoptotic state of the cell. Extracellular regulated kinases 1 and 2 phosphorylate and thereby inactivate the pro-apoptotic protein BAD at serine residue 112. Serine 112-phosphorylated BAD dissociates from the anti-apoptotic proteins Bcl-2 and BclXL, liberating them to act [93]. Of COX-1, the constitutive isoform, and COX-2, the inducible isoform of cyclooxygenases, COX-2 is overexpressed in adenomatous polyps and adenocarcinoma cells converting arachidonic acid to prostaglandins (and other eicosanoids), inducers of mitosis, cell locomotion (by adherence junction changes in the relationship of ␤-catenins to actin cytoskeleton and cadherin transmembrane cell-to-cell adhesion receptors), and neoangiogenesis by VEGF overexpression in the cell’s microenvironment. Colorectal adenomas already manufacture excessive amounts of COX-2 [94]. Interleukin-1␤ is responsible for COX-2 overexpression in colorectal carcinoma cells [95].

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Cyclooxygenase-2 is overexpressed or upregulated by IL-1␤ in Peutz-Jeghers hamartomas [96] and human colorectal and head and neck carcinomas and in murine gastric adenomas and colon carcinomas; COX-2 is suppressed by celecoxib, refecoxib, and diclofenac. Chemoprevention of colon cancer with COX-2 inhibitors [nonsteriodal anti-inflammatory drugs (NSAIDs)] is now widely practiced, while mature results are awaited. Stromal fibroblasts of colonic carcinomas are enticed to produce IL-1␤ and COX-2 [97]. Cyclooxygenase-2 facilitates VEGF (see Part III) expression by tumor or stromal cells and COX-2 inhibitor NS-398 suppressed this effect [98]. Cyclooxygenase-2 activity in lung cancer correlates with microvessel density, VEGF expression, and tumor size [99]. Insulinlike growth factor-II and angiotensin II induce Akt phosphorylation in colon cancer cells [100]. Indomethacin, celecoxib (vide infra), wortmannin, or LY294002 suppress prostaglandin (PG)E-2 production and inhibit tumor cell growth. Cyclooxygenase-2 of tumor cell origin suppresses the antigen-presenting function of DCs [101]. Prostate cancer cells enlist platelet type 12 lipooxygenase (LOX) as their growth factor; these cells express integrins (␣v␤3,5) and anti-integrin monoclonal antibodies (Chemicon) induced their apoptotic death [102,103]. Lipooxygenase inhibitors are baicalein (Biomol) and benzylhydroxy-phenyl pentamide (Biomide). The ‘‘scull-cap’’ from Lake Baikal yields the flavonoid baicalin that inhibits LOXs and Raf-1–mediated phosphorylating signal transductions. Lipooxygenase-producing pancreatic carcinoma xenografts suffered apoptotic death through the mitochondrial pathway upon exposure to LOX inhibitors nordihydroguaiaretic acid, Rev-5901, and baicalein [104–106]. Co-expression of COX-2 and MMP-2 in kidney carcinoma cells contributes to neoangiogenesis [107]. Ovarian carcinoma cells overexpressing COX-2 are chemotherapy-resistant and neoangiogenic [108,109]. Endothelial cells within lung cancers overexpress COX-2 but COX-2 expression by lung tumor cells did not predict higher incidence of brain metastases [99–112]. Cyclooxygenase-2 expression directly correlates with the intensity of neovasculature in breast cancers: COX-2, VEGF, and cyclin D1 are often co-expressed. Cyclooxygenase-2–positive ductal


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carcinomas in situ exhibit higher nuclear grades, and COX inhibitors licensed to treat arthritis may have a role in prevention of breast cancer. Because COX-2 also increases aromatase production, its inhibition by NSAIDs may suppress (chemoprevention) in situ breast cancers [113–118]. Nonsteroidal Anti-inflammatory Agents Epidermal growth factor-R and ERK/MAPK inhibitors U0126 and COX inhibitors (sulindac, acetylsalicylic acid, celecoxib, rofecoxib, indomethacin, ibuprofen) induce apoptotic death in colonic adenoma and xenografted adenocarcinoma cells [93,119]. Ursodecholic acid is an inhibitor of ras gene product proteins and COX-2 in colon carcinoma cells [120]. Diclofenac, a dual inhibitor of COX-1 and COX-2, given in drinking water, inhibited the growth of murine colon carcinoma in vivo [121]. Benzylamide sulindac analogues (CP461) induce apoptotic death of CLL cells [122]. Sulindac sulfide inhibits Se112 phosphorylation of the Bcl-2/BclXL-associated death promoter BAD; dephosphorylated BAD enhances apoptosis. BAD phosphorylated at serine 136 is anti-apoptotic; its phosphorylation at serine 128 results in enhanced pro-apoptotic activity [93]. To be fully effective, NSAIDs should disconnect COX-2 expression regulated by the Wnt pathway as well (see Part IV) [123]. The selective COX-2 inhibitor JT-522 (Japan Tobacco Inc, Tokyo) inhibited the growth of NSCLC cells both in tissue cultures and in xenografts; it inhibited endothelial cells and their inducer bFGF [124]. Exisulind (sulindac sulfone, Aptosyn) is pro-apoptotic, exerting its effect without COX 1 or COX 2 inhibition; it induced apoptosis in human NSCLC orthotopic xenografts and synergized with docetaxel. Exisulind analogues CP461 and CP-255 are broad-spectrum tumor-inhibitory agents acting by suppressing Raf and NF␬B. These drugs are active when administered orally and induced long stabilization of metastatic solid tumors in Phase I clinical trials. Tumor suppressor efficacy of exisulinds encompasses adenocarcinomas of the breast, colon, esophagus, lung, and prostate; squamous carcinomas; and gliomas [125–130]. Celecoxib (or rofecoxib) acts additively in patients with paclitaxel, a carboplatin, against NSCLC by reducing PGE2

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synthesis in the microenvironment of the tumor. Cyclooxygenase-2 inhibitors increase tumor cell radiosensitivity. Doses of celecoxib lower than that of sulindac killed human head and nack squamous carcinoma cells and synergized with chemotherapeuticals [131–134]. Sulindac augmented apoptosis induction of TNF␣ in xenografts of human lung cancer cells and, in orthotopically xenotransplanted human lung cancer cells, it exerted augmenting effects on docetaxel-induced remissions, resulting in prolonged survival [135]. The COX-2 inhibitor SC236 (Pharmacia-Upjohn ; Searle/Monsanto, Skokie, IL) in combination with EGF-R inhibitor ZD1839 (Iressa) and a PKA antisense oligonucleotide (AS-PKAI) synergized with each other against human lung and breast cancer cells grown in soft agar or as xenografts in nude mice [136]. The p185neu (from HER2/neu) TKI emodin synergized with celecoxib in rat cholangiocarcinoma cells [133]. The selective COX-2 inhibitor NS-398 (Sigma Pharmaceuticals, South Croydon, Australia; Cayman Chemicals, Ann Arbor, MI) suppresses the proliferation of oral squamous carcinoma cells and hepatocellular carcinoma cells; in the latter tumor, the malignant cells overexpressed FasL and underwent self-induced apoptosis [137,138]. The exisulind (sulindac) analog CP-461 is a pro-apoptotic inhibitor of PKC (vide supra) and NF␬B; in an AUC (area under the curve) of 200 to 800 mg/day dosage range, it induced prolonged stable disease in patients with advanced solid tumors (colon cancer) [125,139]. If efficacy of rofecoxib in suppressing murine colon carcinoma metastases can be translated to humans, the mechanisms of action included suppression of PGE2 and IL-10 and induction of IL-12 [140]. ZD1839 (Iressa, see Part I) and COX-2 inhibitor SC236 caused apoptotic death of HER2/neuⳭ breast cancer cells [141]. Doxycycline acting as a MMP inhibitor and celecoxib in combination suppressed the growth of osteosarcoma and rhabdomyosarcoma xenografts [142]. In breast cancer cells, COX-inhibitors upregulated ceramide expression, a pro-apoptotic event [143]. In comparison, in clinical trials, intratumorally injected ONYX-015 in combination with gemcitabine given i.v. for the treatment of nonresectable pancreatic carcinoma induced 2 PR, 2 MR, and 6 stabilizations of disease against 11cases with


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progressions of disease. For adenoviral therapy of human tumors, the tumor cells have to express the coxsackie-adenovirus receptor hCAR (see Part I). Conditionally replication-competent adenoviruses have been constructed (COX-2 CRAds); their E1A expression depends on overexpressed COX-2, which is a feature of ras-driven tumor cells: The E3ⳮ Ad-E1A-COX replicates almost exclusively in H-ras–driven tumor cells and is oncolytic in tumor cells with an overactive MAPK pathway. Adenoviral vectors delivering HSV tk gene into tumor cells (AdCOX-2MTk) render tumor cells susceptible to ganciclovir in the HSV-TK/GCV protocols [144–147]. Cyclooxygenase-2 inhibitors and oncolytic viruses may act additively or synergistically in the tumor-bearing human host. RECENT DEVELOPMENTS IN MOLECULAR ONCOLOGY: PARTS I AND II In signet-ring colorectal carcinomas, codon 12 and 13 ras gene mutations are infrequent, but a new A:T transversion at the third base of K-ras codon 61 (CAA to CAT; Gln to His) emerges [148]; would these tumors support the growth of oncolytic viruses? Ras-CAAX and its interactions with FT inhibitors are depicted and explained; FT inhibitors are tabulated and, in conclusion, FT inhibitors in rational combination with cytotoxic chemotherapy are recommended [149]; would FT inhibitors antagonize or act additively with oncolytic viruses? Farnesyl transferase inhibitor SCH66336 acts as a pro-apoptotic and chemotherapy-sensitizing agent in melanoma cells [150]. Tipifarnib (R115777, Zarnestra, Johnson & Johnson, New Brunswick, NJ) and gemcitabine induce PR in patients with pancreatic and nasopharyngeal carcinomas [151]. Overexpression of ␤-catenin in colon cancer cells is a nearly ubiquitous event; sulindac induces degradation of this oncoprotein in the proteasomes [152]. Interactions of Bcr-Abl kinases with translation regulator protein S6 and with the mammalian target of rapamycin (mTOR) are explained [153]. Although point mutations of the bcr-abl fused gene render CML cells imatinib-resistant, these

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cells remain susceptible to pyrido-pyrimidine inhibitors (PD173955; PD166326) [154]. Imatinib does not protect PhⳭ ALL patients from CNS relapses: CNS prophylaxis remains obligatory [155]. In GIST, kit gene mutations are further analyzed to show that exon 9 mutations predict large and recurrent tumors [156]. The EGF-R is targeted by monoclonal antibodies and immunotoxins [157] and by small molecular inhibitors of its tyrosine kinase signal transduction [158]. Gefitinib-resistant breast adenocarcinoma cells (MDA-468) regained susceptibility to the drug after transfection with lipofectamine 2000 (Invitrogen), reinserting the tumor suppressor gene PTEN, or by suppressing the PI3K/Akt pathway with LY294002 [159]. 5′-deoxy-5-fluorouridine (5′-DFUR) and ZD1839 (gefitinib, Iressa) interact synergistically. Iressa potentiates radiation sensitivity of human tumor xenografts. Internal tandem duplication (a D835Y substitution) in AML cells is treatable with FLT3 tyrosine kinase indolinone inhibitors SU5416 and SU11248, which also target VEGF-R; with the piperazinyl quinazoline CT53518; with the indolocarbazole CEP-701; or with the staurosporine-derivative PKC412. This latter compound also inhibits VEGF-R, PDGF-R, and c-kit tyrosine kinase, reduces blast cell count, and induces PR (but not without toxicity) [160,161]. FTL3-mutated leukemic cells are susceptible to herbimycin and geldanamycin (17-AAG) [162,163]. The histone deacetylase inhibitor apicidin induces internal (mitochondrial) apoptosis in Ph chromosome-positive CML cells [164]. The CDK inhibitor flavopiridol interacts with the Rb/E2F-1 system, causing persistent expression of dephosphorylated E2F-1, thereby inducing apoptotic death of Rbdeficient tumor cells. The CDK-1 inhibitors BMI-1026 and BMI-1042 (Laboratory of Metabolism, Center Cancer Research, NCI, Bethesda, Maryland) arrest tumor cells in G2-M, leading to apoptosis (for Cancer Res 2003; 63:7384 See Erratum in Cancer Res 2004; 64:3725). Breast cancer resistance protein (BCRP), its relationship to P-gp (P-glycoprotein product of the MDR-1 gene), and its overexpression in FP-resistant AL cells are explained. Lung cancer cells (SCLC) exposed to flavopiridol in vitro die apoptotic death [167–168].


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The histone deacetylase inhibitor SAHA given i.v. induced MR in patients with chemotherapy-resistant bladder and breast cancers and Hodgkin’s disease [169]. Apicidin (Calbiochem) induces mitochondrial apoptosis in Bcr-AblⳭ CML cells [164]. Suberoylanilide hydroxamide acid or trichostatin (TSA) increased susceptibility of various tumor cells to a long list of chemotherapeutical agents [170]. Epothilone (EPO906) deriving from the myxobacterium Sorangium cellulosum causes mitotic arrest and microtubular derangements in cultured breast cancer cells [171]; STI571 (imatinib) suppresses receptors c-Kit and PDGF and enhances the therapeutc index of epothilone [172]. Lamellarin D isolated from the marine mollusk Lamellaria emerges as a potent new inhibitor of topoisomerase I [173]. The macrocyclic lactone bryostatin isolated from Bugula neritina (maritima) stimulates COX-2 transcription, an observation calling for protocols in which bryostatin is combined with COX-2 inhibitors. Cyclooxygenase-2 upregulates VEGF expression and stimulates neoangiogenesis in gastric carcinoma. Celecoxib induces nuclear localization of p53 in colon cancer cells, a pro-apoptotic event. In premalignant lesions of the oral cavity, COX-2 is already overexpressed, an observation calling for its inhibitors to be used to prevent malignant transformation. Rofecoxib effectively reduced the number and size of rectal polyps in patients with familial adenomatous polyposis [174–178]. Exisulind in combination with capecitabine failed to significantly improve response rate in patients with metastatic breast cancer [126]. Uterine cervical cancer cells express peroxisome proliferator-activated receptor-␥ (PPAR␥), but binding its cognate ligand results in downregulation of COX-2 [179] (Tables 2 and 3). Reasons for the increased virulence of acquired immunodeficiency syndrome (AIDS)-associated Kaposi’s sarcoma (KS) in comparison with the relative indolence of classical KS [180,181] begin to unfold. In addition to immunodeficiency in AIDS occurring because of the depletion of CD4/CD8 T cells, the human immunodeficiency virus (HIV)-1 structural protein Tat induces the overexpression of metalloproteinases in KS cells and, by activating the PI3K/Akt pathway, it secures the

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Table 2 Prominent Targets and Molecular Inhibitors Targets Bcr/Abl fusion oncoprotein basic fibroblast growth factor (bFGF) benzodiazepine receptor Bcl-2 Bradykinin BRAF kinase cycline-dependent kinase I (CDK-I) cycline deacetylase c-Kit CD117 R for stem cell factor c-MET R for hepatocyte growth factor/scatter factor (HGF/SF) cyclooxygenase-2 (COX-2) lipooxygenase (LOX)

CXCL12/SDF-1 chemokine stroma-derived factor-1 epidermal GF receptor (EGF-R)

EGF-R/HER2 Erb2 kinase extracellular signalregulated kinase (ERK) farnesyl transferase (FT)

Inhibitors STI-571 imatinib mesylate, Gleevec) PD166326 PD173955 PD180940 PD173074 PD166285 baicalein PK11195 HA-14-1 antisense oligonucleotides CU201 (B9870) U0126 CI-1040 PD184352 UCN-01 NMI-1026 BMI-1042 flavopiridols BMI-1026 BMI-1042 STI-571 ZD1839 OSI-774 SU11248 PHA-665752 SU11271 SU11606

U0126 sulindac & analogues CP255 CP 248 CP461 Exisulind Aptosyn celecoxib rofecoxib diclofenac ursodecholic acid indomethacin acetyl salicylic acid ibuprofen JT-522 SC-236 NS-398 nordihydroguaiaretic acid Rev-5901 NSC651016 (Suradista) distamycin PNU-145156E ZD1839 gefitinib Iressa OSI-774 erlotinib Tarceva PK11166 CCP-358,774 GW2016 SU11248 AG1478 GW572016 (Tables 5 & 6) CP-65477 CI1033 PD98059 R115777 tipifarnib Zarnestra SCH66336 lonafarnib Sarasar L778123 L774123 SCH44342 PD083176 PD98059 BMS-214662 BMS-186511 SU11248 SU5416 LB42722 FT-277 B956 B1086 (Continued)


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Table 2 Continued Targets fm-like tyrosine kinase-3 (FLT-3) HER2/neu histone deacetylase (HDAC)

h telomerase reverse transcriptase (hTERT) insulin-like growth factor receptor-I (IGF-R) Janus kinase (JAK) neutrophilic factor (NF␬B) matrix metalloproteinases (MMP) mitogen-activated protein kinase (MAPK) mTOR (target of rapamycin) protein kinase C (PKC) platelet-derived growth factor receptor (PDGF-R) phosphatidyl inositol-3 kinase (PI3K) proteasome Raf kinase Ras kinase Rb protein phosphorylated Rho G-triphosphatase (GTP) Rho kinase signal transducer/activator of transcription (STAT) proteins

Inhibitors GTP14564 SU11248 SU5416 MLNS18 PKC412 CT53518 PKC412 herbimycins geldanamycins PKI166 CI1033 GW572016 aphicidin depsipeptide trichostatins suberoylanilide hydroxamide (SAHA) sodium butyrate oxamflatin FR901228 MS-275 rapamycins tyrphostins AG1024 enalapril perindoprilat candesartan (CV11974) AG490 cytokine signaling suppressor proteins (SOCS) PS-341 BAY12-9566 AG3340 Æ-941 (BMS-275291, Neovastat) ONO-4817 CP255 CP461 testicans PD98059 GGTI-298 FTI-277 rapamycins CCI-779 RAD001 PKC-412 UCN-01 ISIS 3521 quercetin bryostatin STI571 (imatibib mesylate, Gleevec) CT52923 SU11248 AG-013736 LY294002 PD98059 wortmannin genistein PS-341 (bortezomib, Velcade) L779450 BAY43-9006 LY294002 tyrphostin AG1024 L774123 L774832 L27632 cucurbitacin antisense oligonucleotides protein tyrosine phosphatases (SHP1,2) phosphotyrosyl peptides SOCS PIAS: proteins inhibitory to activated STAT (Continued)

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Table 2 Continued Targets Rho-associated kinase Src kinase vascular endothel GFreceptor (VEGF-R) VEGF system Wnt signaling

Inhibitors L27632 STI571 Y27632 PD1666326 PD173955 PD180970 SU6656 SKI-606 CP-547,632 VGA1155 CEP7055 SU11248 SU5416 SU6668 PTK787/ZK222584/ZD6474 ZD6126 (NG453) ZD6474 ZD4190 ZK222584 PNU-145156E AG-013736 dickkopf gene product protein DKK1

anti-apoptotic state of these cells. Highly active anti-retroviral therapy (HAART), with inhibitors of viral reverse transcriptase, viral packaging, virus and cell membrane fusion, and viral protease, ameliorates the clinical course of AIDSKS, because it also allows for restoration of NK and T cell counts [182–184]. Reactivation of latent or newly acquired HHV-8 in both classical and AIDS-KS initiates the process. The HHV-8-encoded protein ORF-74 transforms fibroblasts and endothelial cells. The HHV-8-encoded vFLIP (FLICEinhibitory protein), also referred to as K13, activates the anti-apoptotic NF␬B pathway. Virally induced para- or autoTable 3 Activators, Promoters, Replacements (APR) Targets benzodiazepine receptor insulin-like growth factor receptor neutrophilic factor (NF␬B) mutated cyclin-dependent kinases peroxisome proliferator-activated nuclear receptor (peroxisome proliferator-activated nuclear receptors)

APR Ro5-4864 (inhibitor PK11195) angiotensin II (inhibitors in Table 2) FLICE* inhibitory protein FLIP flavopiridols L868275 roscovitine ciglitazone poglitazone rosiglitazone troglitazone

* Fas-associated death domain-like IL-1␤-converting enzyme (caspase 8).


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crine growth factors include IFN-␥, IL-6, stem cell factor (c-kit ligand), and bFGF [182,185,186]. Classical KS is a chemotherapy-sensitive tumor; AIDS-KS responds to doxorubicin and paclitaxel [187] but also is treatable with IFN-␣ (not with IFN-␥), metalloproteinase inhibitors, cis-retinoic acid, and neo-angiogenesis inhibitors. The recent demonstration of CD117 (cluster of differentiation) known as c-Kit receptor and PDGF-R on KS cells calls for clinical trials with imatinib mesylate [188–190]. REFERENCES: PART II 1. Vermeulen K, Van Bockstaele DR, Borneman ZN. The cell cycle: a review of replication, deregulation and therapeutic targets in cancer Cell Prolif 2003; 36:131–149. 2. Wishart MJ, Dixon JE. PTEN and myotubularin phosphatases: from 3-phosphoinositide dephosphorylation to disease. Phosphatase and tensin homolog deleted on chromosome ten Trends Cell Biol 2002; 12:579–585. 3. Kim DM, Koo SY, Jeon K, Kim MH, Lee J, Hong CY, Jeong S. Rapid induction of apoptosis by combination of flavopiridol and tumor necrosis factor (TNF)-␣ or TNF-related apoptosisinducing ligand in human cancer cell lines Cancer Res 2003; 63:621–626. 4. Messmann RA, Ullmann CD, Lahusen T, Kalehua A, Wasfy J, Melillo G, Ding I, Headlee D, Figg WD, Sausville EA, Senderowicz AM. Flavopiridol-related proinflammatory syndrome is associated with induction of interleukin-6 Clin Cancer Res 2003; 9:562–570. 5. Yu C, Rahmani M, Dai Y, Conrad D, Krystal G, Dent P, Grant S. The lethal effects of pharmacological cyclin-dependent kinase inhibitors in human leukemia cells proceed through a phosphatidylinositol 3-kinase/Akt-dependent process Cancer Res 2003; 63:1822–1833. 6. Gildea JJ, Seraj MJ, Oxford G, Harding MA, Hampton GM, Moskaluk CA, Frierson HF, Conaway MR, Theodorescu D. RhoGDI2 is an invasion and metastasis suppressor gene in human cancer Cancer Res 2002; 62:6418–6423.

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PART III: ANTISENSE OLIGONUCLEOTIDES AND ANTI-ANGIOGENESIS ANTISENSE OLIGONUCLEOTIDES Viral Blockade Antisense oligonucleotides are synthesized single-stranded DNA sequences of 12 to 25 mononucleotides binding to mRNA via Watson-Crick base-pairing, thereby inhibiting translation in a manner similar to nucleoside analogues (fludarabine, cytarabine, fluorouracil, capecitabine) or nucleobases (thiopurines, deoxyadenosine derivatives, deoxycytidines). The short synthesized DNA sequences hybridize with specific mRNA strands. First, replication of Rous sarcoma virus was blocked in chicken fibroblasts, followed by the inhibition of many— practically all—viruses, among them HTL-I and HIV-1, against which antisense oligonucleotides were tested. Cytomegalovirus retinitis of patients with AIDS is now treatable with the licensed phosphorothioate oligonucleotide fomivirsen (ISIS-2922; Vitravine) (ISIS Pharmaceuticals Carlsbad, CA; Novartis’ CIBA Vision) [1–8]. The oligonucleotide enters the cell through energy-consuming endocytosis and escapes within the cytoplasm from endosomal or lysosomal vesicles. Cleavage of target mRNA from the DNA-RNA heteroduplex in the ribosomes occurs through the action of the endonuclease endogenous RNAase. The antisense oligonucleotide should hybridize

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with mRNA sequences that do not have homology with sequences of healthy genes at the single-stranded AUG site of the mRNA. In phosphorothioates, a sulphur atom in the PO moiety replaces the oxygen atom; in methylphosphonates, CH3 group; in phosphoramitades, amines occupy this position [7–11]. From Anti- to Pro-Apoptosis The Human Genome Project yielded some 100,000 mRNA species and from this large library target sequences can now be selected. The bcl-2 and bclXL gene→mRNA sequences are primary targets. The phosphorothioate Bcl-2 antisense oligonucleotide G3139 (Oblimersen, Genasense, Genta at www.genta.com) is being tested against melanoma, NSCLC, and leukemias. In 21 patients with non-Hodgkin’s lymphoma, one CR, two PR, and nine stabilizations of disease occurred; in nine patients the disease progressed. When given as continuous infusion combined with DTIC (dacarbazine) to patients with melanoma, complete (or almost complete) regression of disease was observed. In combination with rituximab (Rituxan, Idec), it exerted enhanced cytotoxicity toward EBV-induced human lymphoblasts in SCID mice. Bcl-2 is translocated or amplified in B lymphoblasts driven by EBV genomic sequences, especially in lymphoma cells of an immunosuppressed organ transplant recipient, or in patients with AIDS. G3139 exerts antiproliferative and pro-apoptotic effects in xenografted lymphoma cells as it downregulates Bcl-2 expression and cooperates with rituximab. G3139 targets the first six codons of the Bcl-2 mRNA and, while suppressing the lymphoma, may cause thrombocytopenia. G3139 could induce apoptotic death of xenografted imatinib-resistant Bcr-AblⳭ CML blasts. G3139 stimulated IL-12 production in the host harboring human melanoma xenografts, which regressed. A programmable fusogenic vesicle-encapsulated G3139 reduced by 80% Bcl2 expression in human melanoma cells. In PC3 prostatic carcinoma cells, G3139 reduced Bcl-2 expression but failed to induce apoptotic death. A Bcl-2 antisense oligonucleotide targeting hTERT ‘‘devitalized’’ human bladder carcinoma cells in vitro [12–19].


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Kidney carcinoma cells, like many other tumor cells, kill defensive host T cells by secreting TNF␣-related ligands (FasL; TRAIL) [20]; among lymphocyte-killer tumors (melanoma or sarcoma cells) [21], ovarian carcinoma cells exude FasL-containing vesicles, which kill CD3-␹ host T cells [22]. A bcl-2 transgene protects lymphocytes from apoptotic death induced by kidney carcinoma cells [20]. A Fas-receptor agonist antibody (CH-11) in subtoxic doses increases the sensitivity of Fas receptor-expressor sarcoma cells (but not that of normal fibroblasts) to chemotherapy (doxorubicin; paclitaxel) [23]. Although FasL-expressing tumors may escape death by immune T cells of the host, they seldom metastasize and remain immunogenic [24]. Natural killer cells expressing Fas or FasL and the inhibitory killer immunoglobulin-type receptor (KIR2DL/ CD158a) protect kidney carcinoma cells from CD8Ⳮ immune T cells of the host by inducing sustained c-FLIP (the cellular Fas-associated death domainlike IL-1␤ converting enzymelike inhibitory protein) and by downregulating caspase 8. Antibody blocking the NK cell KIR/HCL-Cwd receptor restored the tumor cell-directed cytotoxicity of immune T cells [25]. Cisplatin downregulates c-Flip, restoring tumor cell susceptibility to TRAIL [26]. ISIS3521 (Affinitac, Eli Lilly, www.isispharma.com) is an anti-PKC␣ (see Part II) agent tested against solid tumors. This tetrameric enzyme consists of catalytic (C2) and regulatory (R2) subunits, which are overexpressed in breast cancer. ISIS3521 suppressed the growth of glioblastoma xenografts (see Part V). It induced CR in patients with non-Hodgkin’s lymphoma. When given in combination with paclitaxel and carboplatin for the treatment of metastatic NSCLC, survival of 8 months with chemotherapy alone was prolonged to 18 months in the combination-treated patients. Genasense and mitoxantrone induced PR in patients with hormone-refractory prostate cancers [27]. Soft-tissue sarcoma cells re-express survivin, the IAP family protein that becomes silent in adult life after extensive activity in the fetus. This is an adverse prognostic factor [28]. An open reading frame (ORF K7) of HHV-8, the Kaposi’s sarcoma-associated herpesvirus, encodes a survivinlike protein

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[29]. The replication-defective adenovirus pAd-T34A inhibits survivin expression in a variety of human cancer cells and, upon intratumoral injection, matches the efficacy of doxorubicin or paclitaxel in inducing cell death [30,31]. Telomerase, its reverse transcriptase and protein (hTR; hTERT) (see Part IV) are co-expressed with survivin in sarcoma cells [32]. Phosphorothioate antisense oligodeoxynuleotides (As-ODN) (Invitrogen, Karlsruhe, Germany) inhibit hTERT expression in bladder carcinoma [33]. Perhaps Ad-T34A and As-ODN in combination—with or without doxorubicin or ifosfamide—will cure metastatic soft-tissue sarcoma? Mesothelioma cells are attacked by LAK (lymphokine-activated NK) cells; killed by ganciclovir after insertion of HSV tk gene; and respond to IFN␣␥ or GM-CSF, but remain chemotherapy- and radiotherapy-resistant and incurable [34]. Even metastatic sarcomas sometimes are curable, however [35,36]. Ad-IFN␥ could induce remissions in mesothelioma [37]. In some 87% of mesotheliomas, the anti-apoptotic survivin is overexpressed. Anti-survivin oligonucleotides restored apoptosis-susceptibility in mesothelioma cells by downregulating survivin protein expression [30,31,38]. The growth of EGF-RⳭ mesothelioma cells could also be suppressed by gefitinib (see Part I) [39,40]. SV40 genome-carrier or SV40ⳮ mesotheliomas arise in patients exposed to asbestos. SV40 induces hepatocyte growth factor/scatter factor (HGF/SF) release from mesothelioma cells because of its interaction with proto-oncogenes met and ras. Met is the receptor of this ligand; it was first identified in a human osteosarcoma. The ligand is commonly secreted by mesenchymal cells, whereas the receptor is commonly expressed by epithelial cells. For example, leukocytes infiltrating bronchioalveolar carcinomas secrete HGF/SF, which is captured by Met receptors expressed by the tumor cells (see Part IV)—a paracrine growth loop. Tyrosine kinase signal transduction from Met can be inhibited by small molecules (PHA-665752; SU11271, SU11606, Sugen, Pharmacia; Pfizer). A replication-defective, c-met ribozyme-expressing adenovirus (Ad-v-Met) suppresses the growth of prostate cancer xenografts [41–44]. A c-met ribozyme delivered by an adenovirus inhibited the growth and metastatic potential of prostatic


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carcinoma cells [45]. This vector could suppress mesothelioma cells, if these tumor cells used the HGF/SF⇒Met pathway as an autocrine growth loop. Mesothelioma cells (see Part IV) thrive on the homozygous deletion of the cell-cycle regulatory molecules INK40/ARF: p14ARF is lost and the anti-p53 MDM2 (HMD2 in the human genome: 12q14.3-15) enzyme is overactive and eliminates the p53 protein (an anti-apoptotic event). An antisense oligonucleotide directed at MDM2 oncogene of prostate cancer cells reduced tumor cell proliferation, increased apoptotic death rate and potentiated the effects of irinotecan and paclitaxel [46–49]; it should be tested against mesothelioma cells. Bcl-2 and survivin overexpression protect mesothelioma cells from apoptotic death. Anti–Bcl-2/BclXL and antisurvivin phosphorothioate oligonucleotides targeting the 232–251 nucleotides of the survivin mRNA suppress survivin expression in mesothelioma cells and restore the cell’s susceptibility to apoptosis [30,31,50]. Adenoviruses pAdARF and Adp16INK4A reinsert the homozygously eliminated gene, and adenovirus Ad-mda7 transfects the mda tumor suppressor gene into the genome of mesothelioma cells [51,52]. Imatinib suppresses in mesothelioma cells, the autocrine growth loop of PDGF, and its receptor; pAd-T34A releases cytochrome C from the mitochondria of mesothelioma cells, a pro-apoptotic event. A simian sarcoma retrovirus carries the transduced PDGF gene: c-sis⇒v-sis. Perhaps adenoviruses (AD16INK4A or Ad-mda7 with anti-survivin As-ODN) will cure mesothelioma (Table 4)? In Ewing’s sarcoma cells, IGF-I receptors are overexpressed [53]. These receptors could be downregulated by antibody or by an antisense mRNA expressor plasmid. Ewing’s sarcoma cells so treated showed increased sensitivity to doxorubicin and failed to form tumors in nude mice. Another intervention is the use of IGF-receptor inhibitor AG1024, which accelerates the degradation of phosphorylated Rb protein and restores the cell-cycle–arresting function of Rb. A plasmid-expressing IGF-I–receptor antisense RNA inhibited the growth of xenografted human melanoma cells [54–57]. Adenoviral constructs Ad-IGF-Ir482st and, to a lesser degree, Ad-IGFIr950st suppressed the growth of pancreatic carcinoma xeno-

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Table 4 Mesothelioma Standard therapy not curative (decortication; XRt; chemotherapy: doxorubicin, platinols; taxanes, pemetrexed: PMTX). PMTX (LY231514, Alimta) folate metabolism enzyme inhibitor additive to cisplatin in remission induction1 Pathogenesis: SV40 genome (when present2): p53 p14 Wnt ↑EGF-R Rx: ZD1839 OSI-774 ↑PDGF-R Rx: STI-571 (Tables 2, 5) ↑Survivin Rx: Ad.survivin.As-ODN ↑Bcl-2/BclXL Rx3: As-ODN bcl-2 ↑mdm2 MDM2 ↓p53 Rx: Adenovirus.anti-mdm.As-ODN ↓mda-7 suppressor gene Rx: Ad-mda7 ↑BAX ↑caspase3→apoptosis3 del INK40/ARF ↓p14ARF Rx: Adp14ARF; Adp16INk4A4 ↑c-Met ←HGF/SF Rx: PHA-665752 SU11271 SU11606 (Table 2) Malfunctioning Wnt: ↑glycogen synthetase kinase 3 ␤ ↑␤catenin ↑c-myc ↑cyclinD Rx: HSVtk ←ganciclovir ↑K(keratin)19 gene Rx: liposome pK19-tk ←ganciclovir5 pAd-734A to release mitochondrial cytochrome C→ apoptosis Ad.mIFN␥: ↑LAK cells ↑immune T cells6 Ad.mIFN␤: ↑NK ↑M␾ ↑PMN7 Pro-apoptotic adenoviral gene Rx3: AdBax AdBak Adp53 Persistence of NDV in stabilized intraperitoneal tumor8 As-ODN ⫽ antisense oligonucleotide Wnt ⫽ wingless/int fusion gene MDM ⫽ human equivalent of mouse double minute chromosome ARF ⫽ alternative reading frame INK ⫽ inhibitor of cyclin DK EGF-R ⫽ epidermal growth factor receptor PDGF-R ⫽ platelet-derived growth factor receptor HGF/SF ⫽ hepatocyte GF/scatter factor HSV ⫽ Herpes simplex virus tk ⫽ thymidine kinase gene IFN ⫽ interferon NK ⫽ natural killer MΦ ⫽ macrophage LAK ⫽ lymphokine-activated killer PMN ⫽ polymorphonuclear (leukocytes) BAK, BAX ⫽ pro-apoptotic members of the Bcl-2 protein family.

1 Thoraxklinik, Heidelberg, Germany; University Western Australia, Australia. Medical University S. Carolina, Charleston, SC. 2 Loyola University Cardinal Bernardin CC, Maywood, IL. 3 Section for Thoracic Molecular Oncology, University Texas M. D. Anderson CC, Houston TX. 4 Chang Gung Memorial Hospital, Taipei, Taiwan. 5 Tokyo Medical University, Bunkyo-ku, Tokyo, Japan. 6 Faculté de Medecine Creteil Cedex, Paris, France; Institut Gustave Roussy, Villejuif, France. 7 Thoracic Oncology, University of Pennsylvania, Philadelphia, PA. 8 Hackensack University Medical Center, Hackensack, NJ.

Table 4 Attack on mesothelioma is dominated by virotherapeutical agents


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grafts and enhanced chemo- and radiotherapy sensitivity of these tumors [58]. Tumor growth factor-␣ drives rhabdomyosarcoma cell growth through ligation to EGF-R, but this signal transduction could be inhibited by an anti–EGF-R antisense oligonucleotide [59]. Tumor growth factor-␣, the ligand of EGF-R, induces dimerization of the intracellular domain of the receptor and autophosphorylation of its tyrosine residues. This process is constitutively active in squamous carcinoma cells of the head and neck. An antisense oligonucleotide of the EGF-R mRNA and docetaxel acted additively in reducing autophosphorylation, signal transduction, AKT expression and VEGF secretion, resulting in cessation of growth of tumor xenografts. This combination acted more effectively than TKI or anti–EGF-R monoclonal antibodies [60]. Colony stimulating factor-1 (CSF-1) is produced by tumor-infiltrating macrophages and exerts mitogenic effect in tumor cells overexpressing its receptor, which is encoded by the proto-oncogene c-fms (found first in the McDonough feline sarcoma retrovirus, v-fms). Antisense oligonucleotides directed at mRNA copies of the CSF-1 gene inhibited CSF-1 production of stromal cells and of MMP in colon carcinoma cells [61]. The FTL3-L (Amgen, Thousand Oaks, CA) (see Parts I and II) stimulates hematopoietic cells in the peritoneal cavity to produce IL-12 (and IL-10) in patients with gynecologic tumors; it stabilized the tumor in the case of an intraperitoneal mesothelioma [62]. Newcastle disease virus, on occasion, can stabilize intraperitoneal mesothelioma [63]. Could these two modalities of treatment be combined? Raf-1 encoded by c-raf (3p25) downstream in the Ras→MAPK cascade is inhibited by ISIS5132 antisense oligonucleotid, which prolonged the life of patients with chemotherapyrefractory metastatic tumors. ISIS2503 is an antisense inhibitor of H-ras mRNA; when given in combination with gemcitabine it prolonged the lives of patients with various advanced tumors. Liposomally encapsulated As-ODN targeting RAF-1 signaling increases radiosensitivity of the tumor. BRAF mutations (3p25) are extremely common (80%) in metastatic melanomas and result in the activation of the Ras-Raf-MAPK path-

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way (whereas the inherited form of melanoma is consequential to germline mutation of CDKN2A gene at the locus 9p21); BRAF is not mutated in uveal melanoma [64–69]. The MEK/ ERK1, 2 (mitogen-activated protein kinase; extracellular signal-regulated kinase) inhibitor U0126 suppresses the growth of BRAF-mutated melanoma cells [65,68] and human gallbladder cancer xenografts [70]. BRAF kinase inhibitors (PD184352, CI-1040, staurosporine derivatives UCN-01) are to be tested in early clinical trials in competition or in combination with As-ODN. The phosphorothioate liposomally encapsulated antisense c-myc (Burnaby, British Columbia, Canada) targets cmyc mRNA (INX-6295) (as tested at Regina Elena Cancer Institute, Rome, Italy, in 2001). In human melanoma xenografts, the c-myc As-ODN downregulated Bcl-2 and c-myc and upregulated p53, leading to extensive apoptotic deaths of the tumor cells [71]. Anti–N-myc strategy is used against neuroblastoma cells [72]. When c-myc is knocked out of ovarian carcinoma cells, the tumor cells lose resistance to, and undergo growth arrest by, TGF␤ [73]. An As-ODN, ISIS2503, targets H-ras and acts additively with gemcitabine in patients with metastatic cancers [74]. An anti–c-myb As-ODN is in clinical trial for the treatment of neuroblastoma [72]. The proto-oncogenes c-myb, c-myc, and c-raf were transduced by ancient retroviruses (avian myeloblastosis and myelocytosis and the murine sarcoma MSV3611 retroviruses) [75]. The COX-2 inhibitor SC-236 (Pharmacia-Upjohn) combined with ZD1839 (Iressa, AstraZeneca) and with anti-PKA AS-PKAI hybrid antisense oligonucleotide induced 60% durable CR in nude mice xenografted with human colon carcinoma cells [76]. Cyclooxygenase-17 is the assembly protein of cytochrome C oxydase. It is overexpressed in NSCLC. A synthetic short, double-stranded RNA (siRNA) AS-ODN vector targeting the COX-17 gene and transfecting NSCLC cells (Lipofectam, Invitrogen, Carlsbad, CA) suppressed gene expression [77]. Short, double-stranded RNAs trigger RNA interference, reduce VEGF synthesis in fibrosarcoma cells, and synergize with the tumor-suppressor thrombospondin-1of tumor cell origin [78].


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The FLICE (Fas-associated death-domainlike IL-1␤ converting enzyme) inhibitory protein (FLIP) activates NF␬B and exerts a strong anti-apoptotic effect in tumor cells; so does survivin, and when mRNAs of both are targeted by oligonucleotides, cells’ susceptibility to apoptosis is restored. The fusion oncoprotein p210Bcr-Abl (see Part I) can be attacked by monoclonal antibodies, by oligonucleotides directed at the mRNA emanating from the genes of the translocated (t9;22) fusion oncoprotein, and by the inhibitor of the phosphorylated tyrosine kinase, imatinib mesylate (Gleevec, Novartis). Adenoviral tyrosine kinase has the ligand FGF linked to its knob region; pancreatic carcinoma cells overexpressing FGF-R readily admit this adenoviral vector, which renders them susceptible to ganciclovir-induced death [79]. The antisense oligonucleotide G4ASODN eliminates the expression of the X-linked XIAP in human lung cancer cells, which either undergo spontaneous apoptosis or become increasingly susceptible to chemotherapeuticals (paclitacel, doxorubicin, etoposide, vinorelbine) [80]. Colon cancer xenografts produce CSF-1 to invite macrophages; MMPs produced by macrophages facilitate the growth of the xenografts. Colony stimulating factor-1 antisense oligonucleotides reduced CSF-1 production in the xenografts, depriving them of macrophages and neoangiogenesis: The xenografts remained dormant or regressed [61]. Expression of Hras is inhibited by the antisense oligonucleotide ISIS2503 [74]. The phosphorothioate oliogonucleotides synthesized against VEGF receptors KDR/Flk-1-ASO inhibited the intraperitoneal dissemination of human gastric carcinoma cells in nude mice [81]. The EGF-R antisense plasmid administered in liposomes to mice harboring tumors of a human head and neck squamous carcinoma cell line inhibited tumor growth; endostatin given subcutaneously suppressed neoangiogenesis and synergized with the antisense oligonucleotide in inducing CR [60,82]. The AKR mouse thymoma-inducing retroviral v-akt derives from c-akt. The gene product protein AKT2 is overexpressed in human gastric, pancreatic, and ovarian carcinoma cells, where it interacts with PI3K, PDGF, bFGF, and IGF

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[83,84]. Antisense RNA oligonucleotides abolished AKT2 encoding in pancreatic carcinoma cell lines; cancer cells so treated lost their ability to grow in xenografts [85]. Tumor cells with activated insulin receptor secrete annexin II [86]. The expression of IGF-IR in human melanoma cells was significantly reduced by an antisense RNA or oligodeoxynucleotide directed at the gene of IGF-IR. Melanoma cells so treated could not form xenografted tumors in nude mice [56]. The anti-apoptotic survivin inhibits caspase 9 and is overexpressed in many human cancers, but the tumor-bearing host mobilizes CD8 immune T cells against peptide epitopes of the survivin molecule (see Part II). Antisense cDNA, or adenovirus pAdT34A, downregulate survivin expression in tumor cells [30,31,38]. Oligonucleotide GEM231, targeting PKA (see Part I), is in Phase I and II clinical trials for patients with refractory solid tumors [87]. Antisense strategies can obliterate the PKC pathway (see Part II) [88] or attack telomerase⇒telomere preservation in tumor cells [89]. Tyrphostin (AG1024) promotes the elimination of phosphorylated Rb proteins in melanoma cells and restores the control of the cell cycle [90]. Although histone deacetylase inhibitors activate p21Waf1 [91], an As-ODN directed at p21Waf1/Cip1 (inhibitors of cyclin-dependent kinases) forces breast cancer cells to undergo the programmed death process [92]. Gene expression of cells infected by HIV-1 was inhibited by an AAV vector encoding antisense RNA directed to the trans-activation response (TAR) sequence and to polyadenylation signals of the virus. A trinucleotide RNA bulge of the viral regulatory sequence TAR positioned within the viral long terminal repeat (LTR) binds the viral regulatory protein Tat, which induces a conformational rearrangement of the TAR RNA and stimulates a 100-fold increase in viral RNA replication. In infected cells treated with the AAV vector, no viral replication occurred and the cells suffered no cytotoxic side effects [93,94]. c-myc The ‘‘oncogene from hell’’ [95], c-myc (8q24), was found first in the genome of the acutely transforming avian myelocytomatosis retrovirus MC29 (v-myc), in which it hybridizes with the viral gag gene. It encodes a p62 DNA-binding protein. In


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Burkitt’s lymphoma, c-myc translocates to chromosome 14q32, next to the heavy-chain immunoglobulin locus, but it may translocate to 2p12 or to 22q11, next to the ␬ or ␭ light-chain loci, where it acts liberated from its natural repressors operating at locus 8q24. Not translocated, but amplified, c-myc is overactive in many human tumors, prominently in SCLC, breast carcinomas, and some sarcomas. Janus-faced c-myc is pro-apoptotic in growth factor-deprived cells, but anti-apoptotic in the presence of abundant growth factors. ConA, EGF, IL-2, and PDGF activate c-myc. In embryonal life and ontogenesis, c-myc is expressed in cytotrophoblasts of the placenta and in endo- and mesodermal cells, but becomes silent in differentiated cells. Cycline-dependent kinases and their inhibitors (CDKN2), which are encoded by the frequently mutated ‘‘multiple tumor suppressor gene’’ at 9p13-22, interact with the cMyc gene product protein, allowing uninhibited progression of the cell cycle. Interferon-␣ downregulates c-myc in promyelocytic leukemia cells and malignant melanoma cells, in which chromosome 9p13-22 is frequently mutated. c-Myc suppresses the CDK 4 and 6 inhibitor p15INK4b. Tumor growth factor-␤ antagonizes c-Myc and liberates p15INK4b, but overexpressed c-Myc subverts TGF␤ and p15INK4b and the cell cycle rolls forward uninhibited [96–99]. In ovarian carcinoma cells, c-Myc repression is lost and the tumor cells become insensitive to TGF␤ [71–73]. The c-Myc protein induces reactive oxygen species (ROS), leading to DNA damage and genomic instability, but it counteracts p53-induced growth arrest, so that ineluctable advancement of these cells through S phase ensues. In p53-deficient Saos-2 osteosarcoma cells, c-Myc inhibits NF␬B, which then fails to activate the antioxidant MnSOD (or Nacetyl-cysteine) [96–101]. Inhibitors of c-myc can be as simple as doxycycline inducing irreversible differentiation of c-myc, overexpressing murine osteosarcoma cells into osteocytes. Temporary inactivation of c-myc indicates that oncogene-induced malignant transformation may be reversible and, when the oncogene is reactivated, it may exert pro-apoptotic effects [100,101]. The chemokine CCL6 is regulated by the Myc proteins. Overexpression of CCL6 liberates malignant cells of their growth-

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factor dependence and promotes their metastatic potential [102]. When TGF␤ exerts its antiproliferative effect, it downregulates c-Myc. The Ser/Thr kinase TOR proteins are positioned downstream of PI3K and are targets of rapamycin, an inhibitor of IL-2. Insulin and IGF autophosphorylate IR and IGF-R, which activate the Ras/MAPK/PI3K cascade. The NMyc and IGF systems are cross-linked: IGF activates N-myc. The PI3K inhibitor wortmannin and the TOR (target of rapamycin) inhibitor rapamycin block this reaction; IGF also counteracts the PI3K/AKT inhibitor LY294002. N-Myc is active in neuroblastomas and rapamycin inhibits the proliferation of neuroblastoma cells. Rapamycin-induced apoptosis of rhabdomyosarcoma cells is prevented by IGF. Rapamycin analogues CC1-779 and RAD001 target mTOR and induce apoptotic death of tumor cells (see Part II). In malignant cells (breast, ovarian, pancreatic, and squamous cell carcinomas), TIE (transforming growth factor-␤ inhibitory element) in the c-myc promoter protects c-Myc. Antiestrogens (tamoxifen; ICI182780) arrest c-myc overexpressing breast carcinoma cells by downregulating cyclin D1, CDK4 and 6, while free CDK inhibitors accumulate [103–106]. Antisense oligonucleotides targeting c-myc mRNA inhibit proliferation of cancer cells, including either estrogen receptor positive (ERⳭ) or ERⳮ breast carcinoma cells [107]. Breast cancer, SCLC, hepatoma, Burkitt’s and non-Hodgkin’s lymphomas, and melanoma are awaiting clinical trials with As-ODN [108,109]. ANTI-NEOANGIOGENESIS Vasculogenesis; Angiogenesis The remarkable history indicating that tumor growth depends on its vascular supply dates back to the 1920s and 1930s [110]. Tumors unable to recruit and sustain a supportive vascular network of their own remain dormant. Vasogenic angiogenesis (vasculogenesis) occurs in embryonic life de novo from mesodermal stem cells. Angioblasts of endothelial lineage proliferate, form lumina, and organize themselves into a primitive vascular network under the guidance of VEGF) by forming autocrine growth loops, as they express receptors for these mediators (VEGF-R2 or KDR ⳱ kinase insert domain-contain-


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ing receptor in humans). The eight exons of VEGF-A (chromosome 6), by alternative splicing, produce the VEGF family. Vascular endothelial growth factors mediate vascular sprouting; endothelial cell proliferation, migration, and intussusception; and increase vascular permeability. Their expression is induced by hypoxia, IL-1␤, TGF␤, epidermal growth factor (EGF) and signals emanating from EGF-R. Vascular endothelial growth factor receptors (KDR), in capturing their ligands, induce endothelial cell proliferation [111–113]. Hypoxia induces high levels of carbonic anhydrase 9 (CA9) and promotes VEGF gene expression [114,115]. Hypoxia-inducible factor-1 (HIF-1) protects tumor cells against apoptosis and induces VEGF production in the tumor bed. Tumor cells overexpress thioreduxin (Trx-1), which upregulates HIF-1 production [116]. Kidney carcinoma cells with deleted VHL gene and its gene product protein (pVHL) constitutively express HIF-1; reinsertion of the VHL gene induces tumor cell death [117]. In these and other (breast and colon) carcinoma cells, HIF-1 overproduction is inhibited by PX-12 (methylpropyl-2-imidazolyl disulfide) and the protein pleurotin [118]. The flavoprotein enzyme Trx-1 is induced by TNF␣; it activates NF␬B [116], an anti-apoptotic event. Organotellurium steroids inhibit thioreductases [119]. Neurolipin on glia cells also binds VEGF165 or PlGF-2. VEGF-C and D (but not A) induce lymphangiogenesis. Tumor growth factor-␤1 is stimulatory to VEGF gene transcription in cholangiocarcinoma; the tumor produces VEGF and endothelial cells of the tumor bed express VEGF-R (a paracrine growth loop), whereas the tumor cells use the TGF␤1→R pathway as an autocrine loop [120]. In breast carcinoma cells, estrogens upregulate VEGF production and VEGF-R expression, creating autocrine growth circuits [121]. Activated STAT3 is a major contributor to neoangiogenesis (Figure 3). Platelets store VEGF produced elsewhere and release it where the platelets are consumed [122]. When platelets are transfused in myelo-suppressed patients, is tumor vasculature inadvertently stimulated by exogenous VEGF? Angiogenesis is initiated from a pre-existing vascular plexus. In the process of neoangiogenesis, extracellular matrix is degraded, and endothelial cells proliferate, invade, and dif-

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Figure 3 Figures 1 and 2 (see Part I) depicted the STAT system as a major contributor to the inhibition of proinflammatory cytokines and chemokines and to dendritic cell maturation/differentiation. STATs upregulate c-myc, the cyclins, and the anti-apoptotic survivin.This figure shows the delicate balance of VEGF and bFGF inducers and inhibitors in the cell and gives a rationale for blocking STAT3 and thus reducing neoangiogenesis a tumor cell would otherwise induce. (The permission of Drs. Hua Yu and Richard Jove to reprint these figures from the February 2004 issue of Nature Reviews Cancer, with the approval of the publisher, is hereby gratefully acknowledged.)


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ferentiate after their branches form lumina. Nonsprouting angiogenesis results from intussusception of pre-existing blood vessels. Functional tyrosine kinase receptor TIE-2 (tunica interna endothelial cell kinase) is overexpressed in tumor cells [123–127]. Tunica interna endothelial cell kinase-2 and its agonist angiopoietin-1 (Ang-1) are essential for sprouting neoangiogenesis and for interaction among endothelial cells, smooth muscle cells, and pericytes. Their interaction can be antagonized by the compound muTekdelta FC (␮Tek␦FC) [126]. Soluble sVEGF-A, sVEGF-R, and sTIE-2 are at high levels in cancer patients [122], but these substances are detectable in the blood supply of blood banks [128]. In malignant gliomas, Ang1, Ang-2, VEGF, and TIE-2 are co-expressed [126]. The TIE2 antagonist Ang-2 mediates regression of blood vessels. Could its gene be delivered into tumor cells by a viral vector? EphrinB2 in arteries and ephrinB4 in veins promote interaction of endothelial cells with smooth muscle cells [129]. Small primary tumors, including leukemic cells in the bone marrow themselves, release or induce the release from stromal cells in their microenvironment, of angiogenic growth factors in addition to VEGF. These include basic fibroblast growth factor (bFGF), placental growth factor (PlGF), and TGF␣. Some tumor cells expropriate the entire VEGF→R system and use it as their own autocrine growth loop, with or without an additional autocrine growth circuit using TGF␤ and its receptor [130,131]. In cases in which TGF␤ acts as a growth factor, its blockade is inhibitory to tumor growth [132]. When TGF␤ exerted inhibitory effects on tumor growth, disruption of signaling from its receptor, as in hepatocellular carcinoma, could lead to enhanced malignant behavior [133]. Some other tumors (uveal melanoma cells) may de-differentiate and redifferentiate toward endothelial cell morphology, phenotype, and function, thereby contributing to blood flow within the tumor bed [134,135]. Tumor-induced neoangiogenesis is usually disorganized and inchoate, and as such, is recognizable as the ‘‘tumor blush’’ in angiograms. Vascular permeability factor (now known as VEGF-A) and VEGFs belong to a large family of cytokines stimulatory

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to neoangiogenesis (‘‘serpentine’’ or ‘‘glomeruloid’’ from preexisting blood vessels, both for blood and lymphatic vessels [136,137]. In endometrial carcinoma cells, both tumor and stromal cells express VEGF-D and its receptor VEGF-R-3; the receptor is active in the adjacent stromal cells as well. Myometrial invasiveness of the tumor correlates directly with the expression of VEGF-D and VEGF-R-3 [138]. The understanding of Wnt signaling (ligands to ‘‘fizzled’’ receptors; Fz) in physiological (placenta; wound healing) and pathological (neoplasia; see Parts IV and V) angiogenesis and its relationship to COX-2, MMP-7, and VEGF is taking shape as a new territory to explore [139–142]. The catalytic subunit of PI3K acts as an oncogene in ovarian carcinoma cells, promoting proliferation and inhibiting apoptosis while upregulating VEGF production. The PI3K inhibitor LY294002 suppresses all these effects and restores the susceptibility to apoptosis of the treated tumor cells [143]. Established large primary tumors switch to the production of anti-angiogenic factors—angiostatin, a proteolytic fragment of plasminogen; and endostatin, the COOH-terminal of collagen XVIII—to suppress the growth of their own micrometastases. Rapid growth of these metastases sometimes occurs after the surgical removal of the large primary tumor, inasmuch as the small metastatic tumors are in that stage of their growth in which the production of neoangiogenesis factors, not that of anti-angiogenesis factors, dominates. For example, established endometrial carcinoma switches off VEGF production and switches on angiostatin production [144–146]. In these tumors, there is an operational VEGF-D⇒VEGF-R3 gowth loop. The plasminogen derivative angiostatin (AS), which is now cloned and is expressed in Pichia pastoris, inhibits endothelial cell migration, proliferation, and tube formation; it induces both intrinsic (mitochondrial) and extrinsic apoptosis of vascular endothelial cells [147–149]. Inhibitors of Neoangiogenesis The most important natural angiogenic mediators are VEGF, bFGF, PlGF-2, PDGF, TGF␣, IL-3, IL-8, G-CSF, and, in AIDS–Kaposi’s sarcoma, HIV-1 tat gene product protein Tat. Signaling from VEGF-R runs the PI3K pathway and provides


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protection against apoptosis to replicating vascular endothelial cells by Bcl-2 activation [150,151]. Blockade of VEGF-R in endothelial cells may disrupt similar signal conduction in coexisting tumor cells. The most important natural angiogenesis inhibitors are IFN␣, IFN␤, angiostatin, endostatin, vasostatin, platelet factor-4, thrombospondin-1, IL-12, IL-18, and prothrombin-1 and -2. Placental growth factor acts as an inhibitor of angiogenesis when it forms inactive PlGF/VEGF heterodimers [152,153]. Results of the Entremed-sponsored endostatin–angiostatin clinical trials remain below the high expectations whipped up by irresponsible and premature daily press releases. In the early 1980s, when IFN␣ (but not IFN␥) [154,155] suppressed the growth of AIDS-associated Kaposi’s sarcoma, but failed to reduce HIV-1 viral load or to reconstitute CD4 and CD8 cells, this author suggested that IFN␣ acted as an anti-angiogenic agent by suppressing the int gene family encoding bFGF [156,157]. Unfortunately, an assistant editor rejected his first manuscript. Since then the anti-angiogenic effects of IFN␣ are widely accepted and publicized [158]. Interferon-␣ is now licensed for the treatment of hairy cell leukemia, CML, certain lymphomas and multiple myeloma, Kaposi’s sarcoma, melanoma, and kidney carcinoma and it is used for its anti-neoangiogenic effects in glioblastoma multiforme (see Part V). For patients with SCLC, IFN␣ and IFN␥ failed to prolong survival, except for one cohort of patients in which 22% of patients treated with chemotherapy and IFN␣ survived 2 years, whereas 15% of patients treated with chemotherapy only survived 2 years (ASCO 噛1832 1999). Interferon-␥ retarded the growth of mesothelioma [159] and ovarian carcinoma [160]. In Th1-type tumor rejection, IFN␥ cooperates with IL-12, DCs, immune T cells, and NK cells. As to IL-12 (WyethAyerst), one opinion holds that its mechanism of action consists of upregulation of INF␥; another view considers it inhibitory to IFN␥. If IL-12 acts against Kaposi’s sarcoma, inhibition of IFN␥ is its mechanism of action, given that IFN␥ is an autoand paracrine growth factor of Kaposi’s sarcoma cells; IFN␥

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promotes the growth of endothelial cells in response to the HIV-1 Tat protein [161,162]. Fibroblast-induced angiogenesis could be inhibited by the tissue-inhibitory protein TIMP-3 [163]. Because Kaposi’s sarcoma cells receive paracrine growth factors, would TIMP-3 suppress the growth of this tumor? Newer trials for SCLC include STI-571 (imatinib), ZD1839 (gefitinib) (see Part I); monoclonal antibodies to VEGF, VEGF-R, and gastrin-bombesin (G17DT); VEGF-R and EGF-R inhibitors (ZD6474); the G3139 antisense oligodeoxynucleotide against Bcl-2; the proteasome inhibitor PS-341; and the mTOR inhibitor rapamycin-derivative CI-779 (see Part II). In the majority of NSCLC, COX-2 expression correlated with neovasculogenesis and poor prognosis. Cyclooxygenase-2 inhibitors (see Part II) suppressed tumor cell (sarcoma) growth, not through direct killing of tumor cells, but consequentially to antiproliferative effects on endothelial cells in the tumor bed [165–170]. VEGF-A also transactivates the anti-apoptotic genes of Bcl-2, survivin, and COX-2 [164]. Cyclooxygenase-1 and COX2 inhibitors (see Part II) hinder wound healing on account of neoangiogenesis inhibition. When PlGF-1 forms heterodimers with VEGF-A, it inactivates VEGF-A, whereas PlGF-2 is neoangiogenic and also anti-apoptotic [150,151]. The South African tree Combretum caffrum yielded the tubulin-binding combretastatins (CA)-seeking colchicin receptors. The tubular-binding combretastatins (Oxigene) induce endothelial cell apoptosis by selectively destroying tumor vasculature and disorganizing endothelial cell cytoskeletons. The water-soluble CA4P depolymerizes microtubules of vascular endothelial cells, especially those that form tumor neovasculature. Kaposi’s sarcoma xenografts are readily eliminated in CA4R-treated hosts. In patients, dose-limiting toxicities (over 50 mg/m2) are ataxia, vasovagal syncope, and bowel ischemia [171–176]. The fumagillol derivative (Aspergillus fumigatus) TPN-470 (AGM-147 Pharmaceuticals) suppresses endothelial cell proliferation. It inhibited the growth in vitro and in vivo of several human cancers (transitional cell carcinoma of the urinary bladder, gastric, colonic, pancreatic, renal, endometrial and hepatocellular carcinomas, and melanoma). In a clin-


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ical trial with paclitaxel, TNP-470 induced PR in 25% to 38% of previously treated patients with metastatic solid tumors [177,178]. Paradoxically, FGF-R, upon capturing its cognate ligand FBF, may act as an inhibitor to mitosis in certain breast carcinoma cells [179]. The flavonoid baicalein (see Part II) antagonizes bFGF-induced neoangiogenesis [180]: Could it inadvertently stimulate the growth of FGF-inhibited breast cancer cells? Isoflavones are anti-angiogenic agents [181]. Of other inhibitors of bFGF or its receptor—PD173074 and PD166285—the first is exclusively specific to bFGF-R, whereas the second also blocks PDGF-R [182]. The lipophilic methylated indolinone angiogenesis inhibitor SU5416 (Sugen) performed poorly against kidney carcinoma and soft-tissue sarcomas, inducing stabilization of disease but no CR or PR. SU5416 directed at VEGF-R prevents neoangiogenesis of developing new tumors but is ineffective against the vascular bed of established tumors. It was tested in combination with IFN␣ against kidney carcinom, but the toxicity of the treatment outweighed its benefit. It did not score well in trials against colon and prostate cancers or against hemangioblastoma of the retina. SU6668 and SU5416 inhibit VEGF-R2, but contributed to severe toxicity (pulmonary embolism, myocardial infarction, cerebrovascular accidents), so these compounds are not in any further clinical trials. Monotherapy with the SU preparations, or with VEGF inhibitors PTK787/ZK222584 or ZD6474, is so far not promising. Oncolytic viruses certainly appear to be much safer than these agents. SU5416, a selective inhibitor of KDR (VEGF-R) tyrosine kinase, also inhibits endothelial cell migration induced by PlGF. The indolinone SU11248 (Sugen) counteracts c-Kit, FLT3, flk-1/KDR VEGF-R, and PDGF-R in preclinical trials for SCLC and other tumors [183–186]. Tyrosine kinase inhibitor SU11248 suppresses growth factor receptors for VEGF, PDGF, Kit, and FLT-3 ligands. In 42 patients with advanced solid tumors, SU11248 induced 4 PR, 3 MR, and 23 stabilizations of disease, while 11 patients continued to progress. Fatigue, asthenia, and neutropenia occurred in 21% to 26 % of the patients [187].

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Other molecular inhibitors of the VEGF system in preclinical trials are ZD6126, ZD6474 (aimed at flk-1/KDR VEGFR2), and ZD4190; PTK787/ZK222584; and PNU-145156E. These agents are extensively reviewed [188–198]. ZD1839 (gefitinib, Iressa) has been approved for the treatment of bronchogenic carcinoma [199] (see Part I). Overexpression of VEGF and Flt-1 receptors in gastric carcinoma [200] would render this tumor to be a reasonable candidate for a clinical trial with SU11248 and SU5416 because these compounds inhibit Flt-1 receptors in gastric carcinoma [201]. Gefitinib, in combination with COX-2 inhibitor SC-236 and the antisense oligonucleotide As-PKAI, all given per os to mice bearers of human colon cancer xenografts, induced CR in 60% of these experimental subjects [76]. Joint administration of SU5416 and IFN␣2b to patients with kidney carcinoma failed to improve survival and exerted significant toxicity [202]. In contrast, IFN␣ acted additively with gemcitabine against orthotopically xenografted human pancreatic carcinoma [158]. Blockade of EGF-R could lead to suppressed neoangiogenesis in orthotopically xenografted human kidney cancer [203]. Treatment with PK1166 inhibits autophosphorylation of a tyrosine kinase and suppresses the growth of these human kidney carcinoma xenografts by downregulating IL-8, BCLXL, VEGF, and bFGF. Metastases of this tumor to lungs were inhibited when PK1166 was administered in combination with gemcitabine [203]. The colchicine derivative ZD6126 (NG453) inhibited the growth of xenografted human NSCLC (both adeno- and squamous cell carcinomas) and colorectal, prostatic, ovarian, and breast carcinomas by inducing apoptotic deaths of CD31Ⳮ vascular endothelial cells of the tumors’ microenvironment; it is in Phase I clinical trials. The VEGF-R signaling through tyrosine kinases is inhibited by ZD6474 and ZD4190; these compounds inhibit the growth of ras-mutated breast carcinoma cells and in combination with paclitaxel, they suppressed the growth of human tumor (breast, colon, gastric and ovarian cancer) xenografts. When ZD6474 was given per os to human tumor xenograftbearing mice, it induced regression of the xenografts [188,189]. So far, no major impact on the course of metastatic breast carcinoma occurred: ZD6474 and SU11248, blocking flk-1/


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kKDR (VEGF-R) and FGF-R; ZD6126 (AstraZeneca), an inducer of apoptosis in endothelial cells; 2MEL (2-methoxyestradiol, Introgen Therapeutics), and the ribozyme Angiozyme failed to induce any major remissions [204]. Ecteinascidin (ET)-743 combined with plasminogen-related protein B additively suppresses tumor growth through antagonism exerted on tumor-associated microvessel formation. Ecteinascidin is in clinical trials for metastatic sarcomas [205–209]. A dipeptide L-glutamyl-L-tryptophan (IM862) is anti-angiogenic and exerts systemic effects in patients treated intranasally for AIDS-associated Kaposi’s sarcoma, exhibiting 36% major responses [210]. The bisphosphonate zoledronic acid is in use for the treatment of patients with bone metastases; it reduced circulating VEGF and PDGF levels [211]. The sulfonated distamycin-A derivative suppresses the growth of human tumor xenografts [212–214]. NSC651016 (suradista) antagonizes stromal cell-derived factor 1␣ (CXCL12; SDF-1), the ligand for chemokine receptor CXCR4 (which also serves as a co-receptor for HIV-1 entry). Suradista inhibits endothelial cell chemotaxis and proliferation. The sulfonated distamycin derivative is more effective than suramin as a FGF inhibitor. The ligand SDF-1 promotes breast cancer cell migration through induction of tumor cell pseudopodia. NonHodgkin’s malignant lymphoma cells migrate and proliferate under the effect of SDF-1, but a monoclonal antibody neutralizing CXCR4 inhibits the growth of these lymphoma cells. Some Chinese herbal preparations rich in tannic acid are inhibitory to the SDF-1 (CXCL12→CXCR4 interaction) and suppress the growth of tumor cells that overexpress the receptor [215]. In Auckland, New Zealand, dimethyl xanthenone acetic acid (DMXAA) is in Phase I and II clinical trials; the compound destroys established tumor vasculature [216–218]. The ␤sheet-forming peptide anginex exerts anti-angiogenic effects additively or synergistically with carboplatin or angiostatin in ovarian cancer cells [219,220]. Aplidin blocks VEGF⇒R autocrine loops in human leukemic cells (MOLT) grown as established cell lines [221]. Leukemia cell death occurred because of mitochondrial and FasL⇒CD95 pathway-induced apoptosis [222].

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Human papilloma virus (HPV)-infected keratinocytes and uterine cervical squamous carcinoma cells utilize endothelin and its receptor as an autocrine growth factor and gain resistance to paclitaxel. The vasoconstrictor endothelin (ET) and its receptor, ET(A)R, are frequently expropriated by malignant tumors (ovarian and prostatic carcinomas) to serve as their autocrine growth loop. Atrasentan (ABT-627) inhibits the growth, counteracts the neoangiogenesis-inducing effects and restores the paclitaxel sensitivity of these tumor cells in xenografts. In hormone-refractory prostate cancer, the ET1→R pathway functions as an autocrine growth loop. Atrasentan acts as an ET inhibitor and stabilizes the disease. Side effects are rhinitis, peripheral edema, and anemia. In ovarian carcinoma cell lines or xenografts, atrasentan reduced microvessel density, downregulated VEGF expression and MMP2, and increased the rate of apoptotic tumor cell deaths [223–226]. The aminosterol, squalamine, obtained from the dogfish shark (Squalus acanthias), is not without dose-dependent liver toxicity, but it induced transient tumor regression in patients with synovial cell sarcoma and breast carcinoma. Squalamine does not kill tumor cells in vitro, but in vivo, because of its anti-angiogenic activity, it suppresses tumor growth. It is not acting against VEGF or its receptors; it inhibits sodiumproton exchange pumps of endothelial cells. In patients, 500 mg/m2/day squalamine is tolerated without major toxicity. In patients with NSCLC, squalamine was added to paclitaxel and carboplatin; it was tolerated well and it might have potentiated the effects of chemotherapy [227,228]. The MMP-inhibitor BMS-275291 (Æ-941 Neovastat) is anti-angiogenic and pro-apoptotic to vascular endothelial cells by caspase 3, 8, and 9 activation [229]. MMP inhibitors elicit self-induced apoptosis of Ewing’s sarcoma cells by upregulating and retaining transmembrane FasL [230]. MMP inhibitors other than BMS-275291 (such as BB3103; TIMP-2) expose tumor (Ewing’s sarcoma) cells to apoptosis. The sarcoma cell expresses FasL for its protection; MMP-7 cleaves and solubilizes FasL but when MMP-7 is blocked, FasL is retained and accumulates in the tumor cell, which then commits the act of


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programmed cell death [230]. In patients with kidney carcinoma, Neovastat suppressed MMP and VEGF production, induced angiostatin production, and increased the rate of apoptotic tumor cell deaths [231,232]. The sulfonated distamycinA derivative PNU-145156E, tested in a Phase I clinical trial, induced tumor stabilization in 4 of 29 patients with solid tumors but it did not lower bFGF blood levels, and it caused thrombophlebitis leading to pulmonary embolism [196,214]. However, a tumor as resistant to therapy as chondrosarcoma could be brought to the state of massive cell deaths elicited by a combination of anti-angiogenic and chemotherapeutical agents [233]. Thalidomide (Celgene, Warren, NJ) downregulates VEGF, TNF␣, and bFGF production in the tumor’s microenvironment and proved to be an effective therapeutic agent for multiple myeloma, myelodysplasia, glioblastoma, KS, kidney carcinoma, and other solid tumors (see Part V). Thalidomide (␣-N-phthalylimido-glutarimide) and its tetrafluorinated analogues block bFGF-induced angiogenesis and TNF␣ release from monocytes; these compounds are effective in the pathological entities listed above and in metastatic melanoma [234–238]. The IMID derivatives are in clinical trials (see Part V). Whereas PI3K is a promoter of tumor neoangiogenesis, placenta GF (PlGF) is an antagonist of VEGF. Placenta GF forms nonfunctional PlGF/VEGF heterodimers [152,153]. Angiopoietins 1 and 2 exert more inhibitory than promoting effects on angiogenesis, and by removing pericytes from the vascular wall, angiopoietins may destabilize neovasculature [125,137]. They should be tested in the treatment of hemangiopericytomas, malignant tumors of the pericytes of Zimmermann. VEGF-producing breast cancer cells become estrogen independent [121] as they express constitutively active AKT3 [239] and generate TGF␤ (inhibitory) and VEGF (stimulatory) autocrine growth loops [121,179]. The antiangiogenic thrombospondin-1 (TSP-1) induces radiosensitivity and inhibits the growth of human tumor (melanoma) xenografts [78]. VGF antagonizes TSP-, but small interfering RNA (siRNA), by suppressing VEGF production, re-

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stores the tumor’s susceptibility toTSP-1 [78,240]. Tumor growth factor ␤ blockade [132], growth inhibition and apoptosis induction by staurosporine [241] (see Part II), and treatment with TSP-1 together may subdue some breast cancer cell colonies. In HER2/neu-positive murine breast cancer, ZD1839 and COX-2 inhibitor SC236 exerted strong antitumor effect [242]. However, TGF␤ was inhibitory to the growth of hepatocellular carcinoma cells, which show accelerated malignant behavior upon disruption of TGF␤ signals [133]. For breast carcinoma cells, TGF␤ could be stimulatory to growth [131], whereas the FGF receptor may transmit growth-inhibitory signals [179]; TGF␤ blockade therefore is expected to suppress, but FGF blockade may release from inhibition, the growth potential of these tumor cells. Some chemotherapeutic agents administered frequently in low dosage (doxorubicin, cyclophosphamide, paclitaxel, docetaxel, vincristine) inhibit blood vessel growth. The DC101 anti–VEGF-R2 monoclonal antibody and dose-dense (frequent) low-dose ‘‘metronomic’’ chemotherapy together suppress tumor neovascularization in an additive to synergistic manner [243]. Monoclonal Antibodies Anti-VEGF monoclonal antibody (bevacizumab, Avastin; rhuMab, Genentech) and anti–VEGF-R2 monoclonal antibodies are in use and act additively or even synergize with 5FU in the treatment of colon carcinoma (ASCO 噛3646 2003) [244]. The combination of the humanized anti-VEGF monoclonal antibody (RhuMab anti-VEGF) and chemotherapy (paclitaxel; carboplatin) resulted in increased response rates of NSCLC in Stages III and IV (ASCO 噛1896 2000): Response rates were: chemotherapy alone, 31%; Mab (15 mg/kg) alone, 22%; and chemotherapy with Mab (7.5 mg/kg), and 40%. Median survival in these three groups of patients, in months, was 15, 12, and 18, respectively. However, a few patients with squamous cell carcinoma developed life-threatening pulmonary hemorrhage; therefore this tumor category is not treated at this time with anti-VGF Mab. These monoclonal antibodies may synergize with TKIs (erlotinib) for the treatment of lung adenocarcinomas as well. Rhu-␣-VEGF suppresses the growth of pros-


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tatic carcinoma xenografts [245]. Trastuzumab (Herceptin, Genentech) also inhibits neoangiogenesis. Bevacizumab (Avastin) stabilized disease and induced minor responses in 17% of patients with metastatic breast cancers and acted additively in combination with capecitabine [204]. Capecitabine and bevacizumab induced objective responses in 19% of patients with metastatic breast cancer vs. a 9% response rate for capecitabine alone, but relapses occurred so rapidly that progression-free survival was not improved [246]. Tyrosine kinase inhibitors (see Part I) of signal transduction emanating from EGF-R or from HER2/neu/erbB2 suppress VEGF production in targeted tumor cells. The VEGF-Trap system eradicated the vascular bed of established xenografts [247]. Anaplastic thyroid carcinomas resist chemotherapy with doxorubicin, paclitaxel, and cisplatin (the Mayo Clinics protocol) but may respond to combretastatin or monoclonal antibody to VEGF and thalidomide [248–250]. Adenovirus ONYX enhances radiosensitivity of these tumors [251]. Could ONYX and combretastatin be combined for therapy? The monoclonal antibody infliximab (Remicade, Centocor, Malvern, PA) (Physicians Drug Reference, 2004; pp 11145–1148) neutralizes TNF␣ and thereby pre-empts the induction of those inflammatory and neoangiogenic cytokines that are mobilized by TNF␣; it ameliorates the self-destructive inflammatory processes of rheumatoid arthritis and Crohn’s disease; it has been insinuated but without proof that it contributes to lymphomagenesis. Antisense Technology A 40-bp liposome-encapsulated antisense plasmid aimed at the mRNA of the EGF-R gene administered in combination with endostatin to mice bearing xenografts of human squamous cell carcinomas of the head and neck exerted synergistic antitumor effects [82]. The VEGF-R phosphorothioate antisense oligonucleotide for KDR inhibited the growth of intraperitoneally xenografted human gastric carcinoma cells in nude mice [81]. Another As-ODN targeting VEGF suppresses the growth of mesothelioma xenografts [252]. As microvessel

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density was reduced, tumor cells succumbed to programmed death. The DNA/RNA mixed backbone As-ODN AsPKAI in combination with ZD1839 (gefitinib, Iressa) and with COX-2 inhibitor SC-238 exerts direct antiproliferative and anti-angiogenic effects on human colon carcinoma xenografts [76]. The tat-free retrolentiviral vector PEX (noncatalytic fragment of MMP-2) with HIV-1 gag, pol, and rev genes within VSV envelope blocks bFGF and MMP-2 production, inhibits angiogenesis in the chicken chorioallantoic membrane, and suppresses the growth of xenografted human melanoma cells [253–255]. Binding of MMP-2 to integrin ␣␯␤3 is disrupted and neovascularization is inhibited. Murine leukemia viral vectors fail to transduce nondividing cells, but retrolentiviral vectors could infect both dividing and nondividing cells. Retrolentiviral vectors integrated in the host cell genome exert long-term effects of the transgene. Adenoviral vectors delivering angiostatin or endostatin genes into tumor cells achieve similar effects (see Part I). The HIV-1 Tat protein potentiates bFGF in promoting endothelial cell proliferation mediated by activated MMP-2 in AIDS-associated KS. The recombinant adenovirus (AdTIMP-3) inserting the TIMP-3 gene (tissue inhibitor of metalloproteinase) into endothelial cells suppressed fibroblast-induced neoangiogenesis [256–258] and could kill tumor cells. Of TIMP-1, -2, and -3, TIMP-1 and -2 inhibit vasculogenesis and TIMP-3 is pro-apoptotic for endothelial cells. Spindle cells of AIDS-associated KS express VEGF and form tumors in SCID mice; anti-VEGF Ig suppresses the growth of these tumors [259]. Could AdTIMP-3 and anti-VEGF monoclonal antibody be applied in combination? When VEGF production is suppressed by ds siRNA interference, TSP-1 secreted by the tumor (fibrosarcoma) inhibits further neovascularization of the tumor bed. Melanoma xenografts suppress the growth of their own micrometastases by producing TSP-1. When the TSP-1–producing parent tumor is surgically removed or eliminated by radiotherapy, the hitherto dormant metastases begin to grow. Thrombospondin-1 administered to the tumor-bearing host inhibits the growth of the micrometastases. Thrombospondin-1 given before and during the elimination of the primary tumor suppresses the growth of


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both the primary tumor and its micrometastases. Established tumors produce more VEGF than TSP-1, but VEGF production could be suppressed by a ds siRNA preparation [78,240]. Either endogenously induced (by ds siRNA), or exogenously administered TSP-1 should be administered to patients at the time when large, established primary tumors are removed. Retrovirally mediated siRNA silencing of the HER2/neu oncogene in breast and ovarian carcinoma cells induced cell cycle arrest, decreased PI3K and AKT signaling and cyclin D1 levels, and increased and restored levels of levels of p27 and Rb protein, leading to apoptotic death of the cancer cells [260]. A plasmid encoding the VHL tumor-suppressor protein and the As-ODN directed at hypoxia-inducible factor 1␣ eradicated large lymhomas in mice [117]. The hypoxia-inducible factordependent replicative adenovirus Ad9xHRE1A kills VHL gene-defective kidney cancer cells [261]. The ribozyme Angiozyme (Ribozyme Pharmaceuticals, Boulder, CO) cleaves the flt-1 mRNA for VEGF-R1 but failed to induce remissions in a clinical trial for breast cancer [262]. Angiostatin mediates apoptotic death in vascular endothelial cells [263]; adenoviral vectors are being constructed to insert its gene into the vascular network of the tumor bed. Vaccines Active angiogenic factor-specific immunizations consist of xenogeneic endothelial cell vaccines, DNA vaccines against VEGF-R, and liposomal FGF-2 peptide vaccine [264–266]. Xenogeneic endothelial cell vaccines protect mice against various transplanted tumors (which were antigenically unrelated to the endothelial cells constituting the vaccine) and the immunoprotective effect could be transferred from immune to nonimmune mice with blood serum (antibodies). Liposome-encapsulated FGF peptide vaccines also induced protection against transplanted tumors [266]. Will it be active vascular endothelial-specific immunization with vaccines, or treatment with antibodies (monoclonal antibodies directed at endothelial cells or at their vasculogenic growth factors) or anti-angiogenic molecular mediators, that will control tumor-induced neovascu-

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larity best [267–270]? Tumor necrosis factor-producing cells coated by infliximab (vide supra) are lysed by complement or by NK cells in an ADCC reaction. The TNF family is considered to be a new target for cancer therapy [271]. So are vasculogenic growth factor-producer cells coated by antibodies (exogenously administered or produced by the host vaccinated against the growth factor) that surrender these cells to ADCC-mediated reactions. Although actively replicating tumor cells are susceptible to many oncolytic viruses, would dormant tumors deprived of their blood supply be accessible and, if so, found still vulnerable to a viral attack? REFERENCES, PART III 1. Zamecnik PC, Stephenson ML. Inhibition of Rous sarcoma virus replication and cell transformation by a specific oligodeoxynucleotide Proc Natl Acad Sci U S A 1978; 83:4143–4146. 2. Zamecnik PC, Goodchild J, Taguchi Y, Sarin PS. Inhibition of replication and expression of human T-cell lymphotropic virus type III in cultured cells by exogenous synthetic oligonucleotides complementary to viral RNA Proc Natl Acad Sci U S A 1986; 3:4143–4146. 3. von Ruden T, Gilboa E. Inhibition of human T-cell leukemia virus type I replication in primary human T cells that express antisense RNA J Virol 1989; 63:677–682. 4. Jansen B, Zangemeister-Wittke U. Antisense therapy for cancer - the time of truth Lancet Oncol 2002; 3:672–683. 5. Galmarini CM, Mackey JR, Dumontet C. Nucleoside analogues and nucleobases in cancer treatment Lancet Oncol 2002; 3:415–424. 6. Dias N, Stein CA. Antisense oligonucleotides: basic concepts and mechanisms Mol Cancer Ther 2002; 1:347–355. 7. Uhlmann E, Peyman A. Antisense oligonucleotides, structure and function. In: Meyers RE, Ed.. Molecular Biology and Biotechnology. New York:: Wiley VCH, 1995:38–45. 8. Sazani P, Kole R. Therapeutic potential of antisense oligonucleotides as modulators of alternative splicing J Clin Invest 2003; 112:481–486.


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232. Bukowski RM. AE0–941, a multifunctional antiangiogenic compound: trial in renal cell carcinoma Expert Opin Investig Drugs 2003; 12:1403–1411. 233. Morioka H, Weissbach L, Vogel T, Nielsen GP, Faircloth GT, Shao L, Hornicek FJ. Anti-angiogenesis treatment combined with chemotherapy produces chondrosarcoma necrosis Clin Cancer Res 2003; 9:1211–1217. 234. Amato RJ. Thalidomide: an antineoplastic agent Curr Oncol Rep 2002; 4:56–62. 235. Eisen T. Thalidomide in solid malignancies J Clin Oncol 2002; 20:2607–2609. 236. Marriott JB, Clarke IA, Czajka A, Dredge K, Childs K, Man HW, Schafer P, Govinda S, Muller GW, Stirling DI, Dalgleish AG. A novel subclass of thalidomide analogue with anti-solid tumor activity in which caspase-dependent apoptosis is associated with altered expression of Bcl-2 family proteins Cancer Res 2003; 63:593–599. 237. Mall JW, Philipp AW, Mall W, Pollmann C. Long-term survival of a patient with small-cell lung cancer (SCLC) following treatment with thalidomide and combination chemotherapy Angiogenesis 2002; 5:11–13. 238. Ng SS, Gu¨tschow M, Weiss M, Hauschildt S, Teubert U, Hecker TK, Luzzio FA, Kruger EA, Eger K, Figg WD. Antiangiogenic activity of N-substituted and tetrafluorinated thalidomide analogues Cancer Res 2003; 63:3189–3194. 239. Faridi J, Wang L, Endemann G, Roth RA. Expression of constitutively active Akt-3 in MCF-7 breast cancer cells reverses the estrogen and tamoxifen responsivity of these cells in vivo Clin Cancer Res 2003; 9:2933–2939. 240. Rofstad EK, Henriksen K, Galappathi K, Mathiesen B. Antiangiogenic treatment with thrombospondin-1 enhances primary tumor radiation response and prevents growth of dormant pulmonary micrometastases after curative radiation therapy in human melanoma xenografts Cancer Res 2003; 63: 4055–4061. 241. McKeague AL, Wilson DJ, Nelson J. Staurosporine-induced apoptosis and hydrogen peroxide-induced necrosis in two human breast cell lines Br J Cancer 2003; 88:125–131.


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242. Rosato FE, Dicker A, Burd R, Miller S, Lanza-Jacoby S. Combining the epidermal growth factor (EGF) tyrosine kinase inhibitor ZD1839 with a selective cyclooxygenase (COX)-2 inhibitor SC236, causes a cooperative antitumor effect in breast cancer cells derived from HER2/neu mice J Surg Res 2003; 114:274. 243. Klement G, Huang P, Mayer B, Green SK, Man S, Bohlen P, Hicklin D, Kerbel RS. Differences in therapeutic indexes of combination metronomic chemotherapy and an anti-VEGFR2 antibody in multidrug-resistant human breast cancer xenografts Clin Cancer Res 2002; 8:221–232. 244. Kabbinavar F, Hurwitz HI, Fehrenbacher L, Meropol NJ, Novotny WF, Lieberman G, Griffing S, Bergsland E. Phase II randomized trial comparing bevacizumab plus fluorouracil (FU)/leucovorin (LV) with FU/LV alone in patients with metastatic colorectal cancer J Clin Oncol 2003; 21:60–65. 245. Fox WD, Higgins B, Maiese KM, Drobnjak M, Cordon-Cardo C, Scher HI, Agus DB. Antibody to vascular endothelial growth factor slows growth of an androgen-independent xenograft model of prostate cancer Clin Cancer Res 2002; 8: 3226–3231. 246. Miller KDet al, cited by Schneider BP, Houck WA, G. Sledge. (204). 247. Huang J, Frischer JS, Serur A, Kadenhe A, Yokoi A, McCrudden KW, New T, O’Toole K, Zabski S, Rudge JS, Holash J, Yancopoulos GD, Yamashiro DJ, Kandel JJ. Regression of established tumors and metastases by potent vascular endothelial growth factor blockade Proc Natl Acad Sci USA 2003; 100: 7785–7790. 248. McIver B, Hay ID, Giuffrieda DF, Dvorak CE, Grant CS, Thompson GB, van Heerden JA, Goellner JR. Anaplastic thyroid carcinoma: a 50-year experience at a single institution Surgery 2001; 130:1028–1034. 249. Dziba JM, Marcinek R, Venkataraman G, Rbinson JA, Ain KB. Combretastatin A4 phosphate has primary antineoplastic activity against human anaplastic carcinoma cell lines and xenograft tumors Thyroid 2002; 12:1063–1070. 250. Bauer AJ, Terrell R, Donipathi NK, Patel A, Tuttle RM, Saji M, Ringel MD, Francis GL. Vascular endothelial growth factor

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monoclonal antibody inhibits growth of anaplastic thyroid cancer xenografts in nude mice Thyroid 2002; 12:953–961. 251. Portella G, Pacelli R, Libertini S, Cella L, Vecchio G, Salvatore M, Fusco A. ONYX-015 enhances radiation-induced death of human anaplastic thyroid carcinoma cells J Clin Endocrinol Metab 2003; 88:5027–5032. 252. Massod R, Kundra A, Zhu S, Xia G, Scalia P, Smith DL, Gill PS. Malignant mesothelioma growth inhibition by agents that target the VEGF and VEGF-C autocrine loop Int J Cancer 2003; 104:603–610. 253. Kessler TA, Pfeifer A, Silletti S, Mesters RM, Berdel WE, Verma I, Cheresh D. Matrix metalloproteinase/integrin interactions as target for anti-angiogenic treatment strategies Ann Hematol 2002; 81S2:69–70. 254. Pfeifer A, Kessler T, Silletti S, Cheresh DA, Verma IM. Suppression of angiogenesis by lentiviral delivery of PEX, a noncatalytic fragment of matrix metalloproteinase 2 Proc Natl Acad Sci U S A 2000; 97:12227–12232. 255. Silletti S, Kessler T, Goldberg J, Boger DL, Cheresh DA. Disruption of matrix metalloproteinase 2 binding to integrin␣v␤3 by an organic molecule inhibits angiogenesis and tumor growth in vivo Proc Natl Acad Sci USA 2001; 98:119–124. 256. Toschi E, Barillari G, Sgadari C, Bacigalupo I, Cereseto A, Carlei D, Palladino C, Zietz C, Leone P, Sturzl M, Butto S, Cafaro A, Monini P, Ensoli B. Activation of matrix-metalloproteinase-2 and membrane-type-1-matrix metalloproteinase in endothelial cells and induction of vascular permeability in vivo by human immunodeficiency virus-1 Tat protein and basic fibroblast growth factor Mol Biol Cell 2001; 12:2934–2946. 257. Sgadari C, Barillari G, Toschi E, Carlei D, Bacigalupo I, Baccarini S, Palladino C, Leone P, Bugarini R, Malavasi L, Cafaro A, Falchi M, Valdembri D, Rezza G, Bussolini F, Monini P, Ensolini B. HIV protease inhibitors are potent anti-angiogenic molecules and promote regression of Kaposi sarcoma Nature Med 2002; 8:225–232. 258. Baker AH, George SJ, Zaltsman AB, Murphy G, Newby AC. Inhibition of invasion and induction of apoptotic cell death of


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PART IV. THE PREDICTIVE VALUE OF TISSUE CULTURE AND XENOGRAFT ASSAYS CULTURE SHOCK Tissue Cultures When cells are explanted from their microenvironment of their host [1,2], they may replicate first in an accelerated fashion, but eventually activate growth-inhibitory mechanisms and surrender to the limited life span rules of Hayflick. The inhibitory mechanisms ensue by the activation of p16INK4a and p21Cip1, inhibitors of CDK, and 19ARF, the inducer of p53. In the population of cell cultures, hypotetraploid individual cells with suppressed ARF and/or MDM2, regulators of p53, are selected out. Some cells with nonfunctional p53 bypass the replication block. If Myc or Ras gene product proteins appear on the scene (with or without actual mutation of the corresponding genes), the cell assumes the malignant phenotype. H-ras–transformed cells in suspension and deprived of cellto-substratum contact (anoikis or ‘‘homelessness’’) are exquisitely susceptible to FT inhibitors (see Part I). Tropomyosins (TM) allow cell detachment and promote detachment-induced apoptosis caused by unligated integrins. Tropomyosins are downregulated in primary breast cancers; consequentially,


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tumor cells remain adherent to the supportive stroma. Resistance to anoikis is implicated in the progression of osteosarcoma cells that thwart apoptosis, even when the sarcoma cells are separated from their subverted and tumor-supportive stroma. Adrenoceptor-␣1 antagonists (doxazosin, terazosin) decrease the adhesion of prostate cancer cells to gelatin and collagen and inhibit tumor cell invasiveness. Doxazosin-induced anoikis was counteracted by Bcl-2 overexpression in the tumor cells [3–5]. All these complex events are consequential to the transfer of cell populations, after the disruption of their genuine cell-to-substratum contacts and interrelationships, from their natural host to plastic surfaces of tissue culture flasks, where they are nourished with fetal calf serum-containing media, are exposed to air, and are transilluminated with fluorescent light under the microscope. Explanted cells undergo ‘‘culture shock’’ [6]. Trypsin Trypsinogen expression is frequently silenced in gastric and other cancer cells. The demethylating agent 5-aza-dC and a trichostatin preparation (Sigma) reactivated trypsinogen expression in tumor cells [7]. Tumor cells exposed to trypsin lose cell-surface integrin ␣v expression. Intraperitoneal dissemination of trypsin-treated gastric carcinoma cells is inhibited, whereas tumor cell susceptibility to apoptosis is increased. Thus, cultured tumor cells trypsinized to detach them from glass or plastic surfaces for transfer as suspensions of rounded-up cells may be altered (downregulated) as to their malignant potentials. Yet in vitro cell line models appeared to be somewhat more acceptable predictors regarding the outcome of subsequent in vivo clinical trials of the agents that were tested first in vitro than were murine allograft (xenograft) models [8]. THE TELOMERES ARE GETTING SHORTER Telomerase The enzyme telomerase consists of its reverse transcriptase and protein (hTR; hTERT). It maintains the length of te-

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lomeres at chromosomal ends. Immortalized (or malignantly transformed) cells preserve their remaining telomeres through the action of their constitutively expressed telomerase. Cells undergoing natural senescence gradually lose their telomeres. Exempt from telomere loss are germ cells and some stem cells. Physiological telomere loss is 50 bp to 100 bp during each cell division. The TTAGGG telomere repeats are synthesized at the 3′ ends of the chromosomes by the RNA-containing reverse transcriptase (RT) telomerase. Without telomere preservation, unprotected (uncapped) DNA ends may either induce cell senescence through Rb and p53 activation or join with one another, resulting in fused chromosomes (dicentrics). Overexpressed telomerase, the ribonucleoprotein DNA polymerase, preserves chromosomal length in cancer cells, despite the frequent mitoses these cells go through. Antisense oligonucleotides complementary to the template region and directed at the RNA component of telomerase reduce tumor growth and increase paclitaxel sensitivity of cultured human tumor cells, especially when given in combination with the RT inhibitor 3′azido-3′ deoxythymidine (AZT); however, clinical trial results have not yet been published. Telomerase-specific replicationdeficient oncolytic adenovirus containing hTERT replicates preferantially in cells overexpressing telomerase as it adds TTAGGG repeats onto the 3′ ends of chromosomes (see Part III). In the host, but not in tissue cultures or xenografts, the enzymatic RT catalytic subunit hTERT and RNA (hTR) elicit immune T cell response. Telomerase inhibitors are antisense RNAs antagonizing hTR. Phosphorothioate oligonucleotides or ribozymes target hTR or hTERT mRNAs. Short RNA duplexes exist and interfere with gene expression: siRNAs (see Part III). These dsRNAs, homologous to the RT or its template RNA, inhibit telomerase activity in cancer (colon carcinoma, uterine cervical carcinoma or fibrosarcoma) cells [9,10]. Rapamycins, As-ODN, Lymphocytes The serine-threonine kinase, rapamycin, an inhibitor of mTOR, inactivated mRNA of telomerase in endometrial carcinoma cells. Rapamycin inhibits mTOR kinases that regulate


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the cell cycle and translation and transcription. mTOR is activated when tumor suppressor gene PTEN is eliminated (a frequent event in cancer cells). Rapamycin in nanomolecular concentrations decreases telomerase hTERT mRNA levels. Rapamycin arrests the cell cycle idependently from PTEN: It is active in both PTENⳭ and PTENⳮ tumor cells [11]. By synthesizing the telomeric TTAGGG/GTTAGG repeats to cap chromosomal ends, the ribonucleoprotein enzyme telomerase endows the cell with limitless replicative potential, as it occurs in rejuvenated cells, stem cells, and malignantly transformed cells. The catalytic subunit of telomerase (hTERT) is targeted by As-ODN in bladder cancer cells [9,12]. The genetically engineered adenovirus Ad-RB94 is hTERT promoter-driven and kills tumor cells overexpressing telomerase. In bladder carcinoma cells, telomerase erosion leads to apoptosis, but healthy cells suffer no harm. If IFN␣ protects telomeres by blocking telomere erosion, it may counteract the efficacy of telomeretargeted virotherapy [10,13], either by natural induction or by additional therapeutic administration. The 2′-0-methylethyl oligonucleotide, by binding telomerase RNA template, inhibits the ribonucleoprotein enzyme. Some peptides of hTERT induce MHC class II-restricted recognition by host CD4 lymphocytes [14]; it may be possible to increase this lymphocyte population by administration of a vaccine or IL-2. The oligonucleotide thiophosphoramidate GRN163 arrests the growth of multiple myeloma and lymphoma cells; tumor cells suffer telomerase shortening and undergo senescence. This oligonucleotide hybridizes with human telomerase RNA (hTR); tumor cells treated with GRN163 senesced rapidly and died apoptotic deaths [15–19]. Natural telomere loss may continue in tissue cultures, but a subpopulation of cultured cells may learn to preserve its telomeres. Populations consisting of healthy or reprogrammed stromal cells in admixture with a heterogeneous assembly of tumor cells may perish during the ‘‘culture shock’’ or transform in vitro, whereas a subpopulation of mutated cells endowed with the mechanisms of telomerase reactivation escape senescence and death and proliferate in an immortalized fashion. These are the new cell populations submitted to experimenta-

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tion. Tumor cells established in culture do not represent the entire cell population of the natural tumor that was residing in the microenvironment of its host. Furthermore, the complex interactions of the tumor cells with immune reactions (suppressive or enhancing) of the host are absent in vitro. Drug or oncolytic virus assays of tumor cell populations established in culture or in xenografts may not reflect the responses elicited when tumor-bearing hosts are treated with the same agents in vivo.

ONE DAY IN THE LIFE OF ‘‘IVAN XENOGRAFTOVICH’’* Paracrine Circuits Tumor cell populations consist of individual tumor cells dependent on paracrine growth factors of stromal cell origin and of tumor cells independent of the reprogrammed stroma and able to drive their own growth by autocrine ligand-to-receptor growth loops. This is most evident in cultures of sarcoma cells [20,21]. Tumor cells dependent on paracrine growth factors of stromal cell origin become extremely vulnerable when they are forcefully extricated from their natural environment and are xenotransplanted; a selection process ensues, resulting in the survival of the tumor cell subpopulation that is able to drive its own growth by autocrine growth loops. The gene of human VEGF-A transferred by an adeno-associated viral vector can induce neoangiogenesis in the mouse, but other growth factors may not transgress species barriers: If produced by the xenotransplanted human cells, they may not induce a response in the mouse or, if produced by the new murine host of the

Dedicated to Alexandr Solzhenitsyn on his 85th birthday, after his ‘‘One Day in the Life of Ivan Denisovich’’ in the ‘‘GULAG Arkhipelag’’ of the Soviet Union. In the xenograft, the exiled cancer cell struggles for survival and sustains forceful attacks on its life. Cancer cells are considered to be subversive criminal elements, whereas prisoners of the GULAG were innocent victims of a tyrannical regime that subdued them into the brutality of forced labor camps of immense proportions.


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xenotransplanted human tumor cells, they may not find a cognate receptor in the xenograft to act upon. Let us consider the human bronchioalveolar carcinoma (BAC) of the lung (Table 5) with purported but unproven viral (herpes and retroviral) etiology. Indeed, this multifocal tumor occurring in non-smokers and recurring after excisions, resembles the retrovirally induced jaagsiekte of sheep. Sheep retrovirus RNA or proviral DNA could not be found in the human tumor, but antibodies directed to the capsid proteins of the ovine retrovirus stain the cytoplasms of some human BAC cells. The ovine retroviral provirus DNA transforms rodent fibroblasts [22–26]. A comparable situation exists in the feline host [27]. Human BAC cells express Met receptor, the gene product protein of the c-met proto-oncogene. The avian erythroblastosis retrovirus S13 posseses a related oncogene—the v-sea (for sarcoma, erythroblastosis, and anemia). The cognate ligand for Met is the hepatocyte growth factor (HGF) produced by platelets and neutrophil leukocytes. Bronchioalveolar carcinoma tumors attract neutrophil leukocytes and receive HGF from them [28]. Xenografted BAC tumors may be deprived of such support and therefore succumb readily to a kinase inhibitor that these tumor cells would have resisted in their natural environment. However, Met receptor and HGF antagonists (K252a; HGF/NK4) may suppress these tumors best in their natural environment [29–32]. Ribozyme-carrier adenovirus suppressed the growth of c-met–mutated other (prostate cancer) tumor xenografts [33]. Brochioalveolar carcinoma is considered to be susceptible to gefitinib (Iressa) (see Part I). The cmet oncogene is mutated also in SCLCs [34]. This latter tumor frequently uses the bombesin/gastrin-releasing peptide receptor (BN/GRP) and its ligand for an autocrine growth loop [35]. Monocyte Fc receptor-mediated ADCC, in combination with cisplatin, etoposide, and paclitaxel chemotherapy, acted additively against SCLC. Non-SCLCs are driven by the glycoprotein osteonectin (SPARC; secreted protein acidic and rich in cystein) of stromal cell origin. The locus of the osteonectin gene is at 5q31-33; it dictates cell-matrix interactions during ontogenesis. When reactivated during oncogenesis, its activities correlate with worsening prognosis [36]. Lung adenocarcino-

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Table 5 Target: Epidermal Growth Factor Receptor cetuximab (C225)→ LY294002→

↓ PI3K ↓

PTEN→

Akt

E G F-R ↓ STAT

↓ Ras ↓

←Gefitinib (AstraZeneca) erlotinib (Genentech) ←EKB ⫺589 (W-A) PKI-166 (CGP59326) (N) ←GW2016 (GSK) CI1033 (PD183805) (Pf)

Raf ↓ MEK/MAPK/ERK

U0126→

jun/fos/myc

cyclin D1

anti-apoptosis

neo-angiogenesis invasiveness ↑VEGF ↑MMP-9 ↑bFGF ↑IL ⫺8 EGF-R 170 kD transmembrane protein; dimerizes with HER; ligates EGF & TGF␣. Overexpressed in human neoplasms: H&N squamous cell carcinoma 80%–100%; NSCLC, 40%–80%; prostate cancer, 40%–80%; ovarian cancer 30%–70%; colorectal cancer 20%–70%; pancreatic cancer, 30%–50%; breast cancer, 30%. W-A ⫽ Wyeth-Ayerst; N ⫽ Novartis; GSK ⫽ GlaxoSmithKline; Pf ⫽ Pfizer Summary of clinical trials in advanced NSCLC: standard chemotherapy plus EGF-R inhibitors Response (%) erlotinib gefitinib cetuximab best supportive care PR/CR 12 12–18 22 0 Stabilization 39 31–36 33 no data Overall survival (mo.) 8.4 6.5–7.9 7.6 4.6 Alive at 1 year (%) 40 24 no data 11 Bronchioalveolar carcinoma (BAC): of 50 patients treated with erlotinib 13 responded: 26%; response rate of BAC to gefitinib 38%; to paclitaxel 14%. Median duration of response ⬎6 months. Grade of skin rash positively correlates with survival. Gefitinib and erlotinib: clinical response does not necessarily correlate with grade of EGF-R expression (responding ↓EGF -R tumors; nonresponding ↑EGF -R tumors). Lack of significant additivity to chemotherapy results. In H&N squamous cell carcinoma, ↑EGF -R dictates adverse prognosis. Response to gefitinib correlated with skin reaction; severe: 11 months, none 5 months median survival. Table 5. Data presented at the 10th World Conference on Lung Cancer are based on the bulletin issued on January 2004 by the American Academy of Continuing Medical Education www.academycme.org


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mas evade host immunity by overexpressing FasL to kill host NK and T cells and downregulate IL-13R␣2 to facilitate metastatic growth in the brain [37]. The phytoalexin resveratrol (present in red wine) inhibits the anti-apoptotic NF␬B and the phosphorylation of the Rb protein and suppresses the growth of lung (and other) human cancer cells in xenografts [38,39]. Natural Killer Cells Athymic and other immunodeficient hosts of xenotransplanted human tumors cannot launch an immune T cell-mediated attack on their newly introduced parasite. If tumor cells defended themselves in their natural host by expressing FasL to kill Fas receptor-positive immune T cells of the host [40], now they may safely downregulate the expression of FasL, but may overexpress survivin instead [41]. If the tumor concealed certain tumor antigens (fusion oncoproteins, point mutated oncoproteins, survivin), now these antigens may reappear without being targeted by host immune T cells. The newly transplanted tumor should protect itself against NK cell- and macrophage-mediated attacks of its new host and modify its cell surface accordingly by concealing those antigens that NK cell receptors (KIRs, NKp30, NKp44, NKp46, NKG2D) recognize to escape ADCC reactions of host NK cells and macrophages. Insulinlike Growth Factor-R Tumor cells surviving in their new host may switch from the dominant oncogenic cascade that they used in their natural host to a secondary, substitute cascade serving them better in their new microenvironment [42–46]. For example, tumor cell populations deprived of their natural contact with their matrix (anoikis) undergo apoptotic death unless they switch to EGFR–mediated signal transduction for survival. These cells are exquisitely susceptible to the blockade of EGF-R signal transduction and succumb to it, whereas in their natural environment integrin-linked kinases and IGF factor-induced kinase cascades could have protected them. For example, some colon cancers use IGF and its receptor for an autocrine growth loop.

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Signal transduction from the IGF-R activates the c-src oncogene. Insulinlike growth factor and its binding protein promote the growth of glioblastoma cells. High levels of IGF and its binding protein in the blood predispose to malignant transformations (breast cancer and squamous cell carcinoma of the uterine cervix) [47–50]. Angiotensin II activates the IGF-R. In colon carcinoma cells, the COX/PGE2 pathway activates the IGF-R; these tumor cells produce IGF-II and its ligand for an autocrine growth loop. Angiotensin II inhibitors (enalapril, perindoprilat) downregulate IGF-R expression in colon cancer cells. The growth of prostate cancer xenografts is inhibited by angiotensin II receptor-1 blockade by candesartan (CV11974, Takeda Pharmaceuticals North America, Lincolnshire, IL, subsidiary of Takeda Chemical Industries, Japan) [51,52]. Do xenografted cancer cells continue the production of IGF and express its receptor? If not, these cells become more vulnerable to noxious agents. Differences between EGF-R and IGF-R expression in the tumor’s natural environment and in its new host after xenografting may increase the susceptibility of the tumor cell population surviving in the xenograft to the agents that are being assayed for therapy. Activated Stroma Tumors ‘‘activate the stroma’’ and fibroblasts of the tumor’s native microenvironment express FAP, the fibroblast activation protein, a protease against which a monoclonal antibody (sibrotuzumab) has been developed [53,54]. When we assay for an oncolytic virus, do we check whether the xenograft’s fibroblasts are activated and express FAP? The relationship of melanoma cells and stromal fibroblasts entails direct contact and ‘‘cross-talk’’ by means of molecular mediators and their receptors (cadherins, bFGF, PDGF, VEGF, etc.), resembling a ‘‘conspiracy’’ between tumor and stromal cells [55]. Not only tumor cells but also stromal cells, even when only moderately positive for HER2/neu, and even without HER2 amplification, could react to trastuzumab (Herceptin, Genentech): Treated stromal cells ceased to support breast cancer cell adhesion and growth in co-cultures [56]. There is a formidable


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lack of knowledge regarding the behavior of stromal cells toward the heterologous xenografts. Most of these events, and more, are depicted in a table and in a cartoon [57,58], which propose that a fusion oncoprotein is generated in melanoma cells. The extracellular domain of this putative oncoprotein is supposed to be the Fas receptor (CD95); its intracellular domain is the G-CSF receptor (GCSF-R). Chromosome breaks occurring in melanoma cells at the G-CSF-R and Fas loci (1p32-34 and 10q23-26, respectively) would bring about the formation of this fusion oncoprotein: t(1; 10)(p32-34;q23-26). Attachment of FasL to this receptor would induce cell divisions. The FasL may be part of an autocrine growth circuit of the tumor cell or it may derive from the host. Such a fusion oncoprotein in melanoma cells would make a good target for TKI and monoclonal antibodies. Is it the tumor’s natural environment or its tissue cultures or xenografts that are most conducive to natural hybridoma formation? Intercellular Adhesions It was in the 1940s that Professor T. Huzella published in Hungarian and German his first astute observations on cellmatrix interaction, as he visualized them in his tissue cultures [59]. The Hungarian school continues to make contributions to the understanding of these relationships in a recent volume edited by Eva Klein in Stockholm [60–62]. In elastin-matrix interactions, the tumor cells produce elastin; of proteoglycans, decorin inhibits and perlecan promotes, tumor cell locomotion; and the aging process alters the extracellular matrix, rendering it more favorable for invasion by incipient tumors. Fc receptor expression and metalloproteinase interactions in the tumor bed are major determinants of the host–tumor relationship [63]. Laminin isoforms interact with MMPs [64,65]. Legumain overexpression by the tumor promotes its invasiveness [66]. All these features may be lost or altered in the xenograft. The heterodimeric transmembrane receptors of cell surfaces, the integrins, connect cells and matrix; fibrinogen, fibronectin, vitronectin, and collagens are the major ligands of integrins. Alpha-v integrin inhibitors (the humanized mono-

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clonal antibody Vitaxin directed to ␣v␤3; or cilengitide, mimicking the recognition of the RGD ligand) prevent tumor cell migration [67–70]. The integrin antagonist S247 inhibits the formation of liver metastases by colon carcinoma cells in mice and it is anti-angiogenic [71]. Obtustatin purified from vipera venom is a selective inhibitor of ␣1␤1 integrins [72]. Integrinlinked kinase expression by melanoma cells correlates with enhanced invasiveness and poor prognosis [73]. Periostin (member of the family of axon-guiding proteins in mammals and fascilin in insects) reappears in ovarian carcinoma cells, serves as a ligand to integrins ␣v␤3,5, and mediates tumor cell adhesiveness and migration; anti-integrin monoclonal antibodies counteract its effects [74]. Sugen (SU6668), by antagonizing VEGF-R2, FGF-R1, and PDGF-R, suppresses the intraperitoneal spread of, and ascites formation by, ovarian carcinoma xenografts [75]. Thus, once recognized, factors that promote invasiveness and metastasis formation of tumor cells in their natural microenvironment can be effectively antagonized in vitro and in vivo, as their assays in this case appear to bear clinical validity. Natural Hybridomas Tumor cells under attack within their microenvironment may resort to dramatic escape maneuvers (that may or may not take place in xenografts). When tumor cells express the FasL gene encoding the ligand, they not only may kill host lymphocytes, they may utilize the FasL→Fas receptor system as an autocrine growth loop, such as in human melanoma cells [58,76]. Tumors expressing FasL attract neutrophil leukocyte infiltrates; when rejected, these tumors may immunize their host against live tumor cell challenge. However, these FasLⳭ tumors were able to deflect all host immune reactions when they produced TGF␤ and reduced costimulatory CD80 expression [43,77]. Fusion of tumor cells with subverted defensive or other cells of the host is referred to as ‘‘natural hybridoma formation’’ [78]. Cells of a retrovirus-producer murine lymphoma fused with plasma cells of the host; the tetraploid cells remained highly malignant and continued to secrete the spe-


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cific antiretroviral immunoglobulins originating from the plasma cell component of the fusion product. If it were called ‘‘hybridoma’’ (it was not) at the time when this phenomenon was first observed, reproduced, and reported in 1969–1970, these continuously antibody-producing fused cells would be cited as the very first example of ‘‘natural hybridomas’’ (J. Sinkovics, Chapter 1 in this volume) [79–82]. Committed or noncommitted lymphocytes may fuse with macrophages or DCs (in a case of a murine lymphoma; in AIDS under the effect of HIV-1; in Reed-Sternberg cells under the effect of an asyet-unidentified retrovirus) [83–85]. In the case of a murine sarcoma, lymphocytes ‘‘spontaneously’’ fused with semiallogeneic host macrophages and thereby gained increased malignancy [86]. THE MICROVASCULAR TUMOR BED Microvasculature The microvasculature of the tumor bed, consisting of active vascular endothelial and stromal cells, whether developing or established in the natural host or in xenografts, regulates the influx of nutrients and efflux of metabolites; the degree of hypoxia; and the access or exclusion of lymphocytes, macrophages, antibodies, and chemo- and cytokines to the tumor. Of the VEGF-R family, VEGF-R3/Flt-4 and its ligands VEGFC and VEGF-D induce lymphangiogenesis and spread of tumor cells through lymphatic vessels [87]. Of the molecular mediators in interplay, endostatin exerts, through its COOH terminal fragment inhibitory and through its fragment III, stimulatory effects on new blood vessel formation. Endostatin preparations from Calbiochem (EMD Biosciences, San Diego, CA) and EntreMed (Prince William, MD) differ: Only the former preparation in a HIF-independent manner inhibits endothelial tube formation [88,89]. Vasculogenic agents may be expropriated by malignant cells to function as growth factors: Acute myeloid leukemia cells produce TGF␤ and its receptor, and chronic myelogenous leukemia cells produce VEGF and its receptor for autocrine growth loops [90,91]. The 21 amino acid vasoactive peptides, the ETs, work in breast cancer cells

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as overexpressed autocrine and paracrine growth loops [92,93]. Angiotensin (Ang) 1 and 2 are ligands for Tie 2 (see Part III), and Ang 1 stimulates the glomeruloid microvessel proliferation in the tumor bed of NSCLC [94]. Thrombospondin-1 is anti-angiogenic. Tumors expressing no TSP-1 at their deep invading margins spread and metastasize [95]. Interleukin-10 is referred to as an immunosuppressive cytokine; it inhibits TGF␤dependent neoangiogenesis and downregulates VEGF. Yet its low expression correlates with tumor spread and metastasis formation. VEGF overexpression at the deepest invading edge of a tumor forecasts heavy microvessel density and rapid tumor growth, with short survival of the patient. Low TSP-1 and high VEGF expressing tumor cells exhibit the most rapid rate of expansion. The TSP-1 gene is silenced in neuroblastoma cells by methylation; 5-aza-2-deoxycytidine demethylates the gene and restores TSP-1 expression, with regression of tumor xenografts [96]. Angiogenins and tissue factors, the glycoproteins that initiate blood coagulation, are responsible for the hypervascularization of hepatocellular carcinomas [97,98]. Ovarian carcinoma cells under stress (exposed to norepinephrine) increase their VEGF production; the process is reversed by propranolol [99]. The hemangioblasts of VHL disease are VHL gene-defective neoplastic cells that co-express erythropoietin receptors and ligands for an autocrine growth loop, but they may differentiate toward erythrocyte (red blood cell) formation [100]. Vascular mimicry practiced by melanoma cells is modulated by the tissue factor pathway inhibitors-1 and 2 (TFPI-1 and -2) and may be inhibited by antibody to TFPI-1 or TFPI-2 [101]. The tumor microvasculature may form a barrier to antitumor immune reactions of the host. Histamine receptor antagonists famotidine and cimetidine allow transgression of the barrier by tumor-infiltrating immune T cells [102]. Solubilized Flt-1/VEGF-R1 inhibits HER2/neuⳭ mouse mammary tumor growth. Immune T cells directed at HER2/neu antigens were most efficient in suppressing tumor growth in mice that were overproducing sFlt-1 [103]. Suppressors Antiangiogenic agents include the COX-2 inhibitors celecoxib [104] and SU5416 (Sugen) [105]. Treated cervical or lung can-


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cer cells fail to produce prostaglandins. The dipeptide boronate proteasome inhibitor PS-341 (Proscript, Millenium Pharmaceuticals) inhibits NF␬B activation, depriving pancreatic cancer cells of an anti-apoptotic survival mechanism [106]. The dithiolethione antischistosomal agent oltipraz inhibited the growth of a murine angiosarcoma [107]. CP-547,632 (Pfizer) inhibits autophosphorylation of tyrosine kinases and their signal transmittal from VEGF-R-2 and from bFGF-R. It is strongly anti-angiogenic [108]. VGA1155 (Taisho Pharmaceuticals, Tokyo, Japan) blocks binding of VEGF to receptor KDR/ Flk-1 [109]. The synthetic glycine ester CEP-7055 (Cephalon, USA; Sanofi, France) decreased microvessel density and inhibited the growth of glioblastoma, breast, colon, lung, pancreatic, and prostate cancers and an angiosarcoma in xenografts [110]. Orthotopic human pancreatic cancer xenografts are suppressed by a VEGF-neutralizing antibody [111]. The growth of orthotopic human breast cancer xenografts is inhibited by a monoclonal antibody blocking VEGF binding to VEGF-R2 (KDR/Flk-1) [112]. EntreMed’s rh-angiostatin given twice daily subcutaneously was nontoxic and stabilized advanced cancers in 6 of 24 patients [113]. Platelet-activating factor (PAF) mediates inflammatory cytokines and vasculogenesis. It is inactivated by the enzyme PAF-acetylhydrolase (AH). Kaposi’s sarcoma xenografts transfected to overexpress PAFAH grew very slowly because of the lack of neovascularization [114]. It appears that most established xenografts elicited neovascularization, so agents that act against formed blood vessels can be reliably tested in this system; suppression of new blood vessel formation during the first days after xenograft implantation is much more difficult to interpret correctly. CHEMOKINE AND CYTOKINE GROWTH FACTORS Expropriated Cytokines Tumor cells expropriate inflammatory cytokines for their autoor paracrine-driven growth loops. These growth factors may not be readily available to them in their new microenviron-

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ment. Examples of cytokine and other common growth factors expropriated by tumors for their own growth advantage have been cited elsewhere (J. Sinkovics, Chapter 1 in this volume) [115,116]. Tumor cells can convert molecular mediators that are physiological inducers of cell death to serve as their growth factors: TNF␣ for neuroblastoma and melanoma [117]; FasL for melanoma [58,76]; IL-2 for T cell lymphoma-leukemia and for some melanomas; IL-6 for Kaposi’s sarcoma, multiple myeloma, kidney carcinoma, and hormone-refractory prostatic carcinoma [118]; IL-7 for Se´zary cell lymhoma and cutaneous T cell lymphomas; IL-8 for Kaposi’s sarcoma [119]; IFN-␥ for B-CLL [120], Kaposi’s sarcoma, and some osteosarcomas (see Part III). In contrast, IFN␥ exerted cytotoxicity on ovarian carcinoma and mesothelioma cells [121,122]. In ovarian carcinoma patients in clinical trials, INF-␥ could induce PR [122]. Interferon-␥ cooperates with IL-12 in inducing Th1-type antitumor immunity [123]. Low levels of IFN-␥ are generated in the bladder mucosa during BCG treatment of bladder carcinoma. High levels of INF-␥ are tumor suppressive, but low levels may serve as growth factors for the tumor [124]. Hormone receptor-negative breast cancer cells overproduce IL-1␣ and attract metalloproteinases to facilitate tumor cell invasiveness [125]. Some melanoma cells produce constitutively IL-1. The natural IL-1R antagonist IL-1ra suppressed the metastatic potential of these melanoma xenografts [126]. Autocrine production of IL-4 and IL-10 by thyroid carcinoma cells upregulates Bcl-2 and BclXL, rendering tumor cells to be chemotherapy-resistant [127]. Interleuken-6 soluble receptor and TGF␤ blood levels are high in patients with prostate cancer and correlate with adverse postoperative prognosis [128]. Interleuken-6 may be neutralized by monoclonal antibodies BE-8 or CNTO328 in clinical trials for those tumors in which IL-6 may have a promotional role [129]. Interleukin-8 protects ovarian carcinoma cells against the TNF␣-related apoptosisinducing ligand TRAIL-induced apoptosis [130]. The double agent IL-10 displays a dual role in tumor immunology [131]. While it stimulates NK cells, it suppresses the maturation of DC. Antigens presented by immature DC are often tolerogenic, whereas antigens presented by mature DC are immunogenic.


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In some gastric cancers, EBV-induced small RNA mediates a mitotic cascade [132]. In some Burkitt lymphoma cell lines (Akita), EBER-induced IL-10 acts as an autocrine growth factor [133]. Interleukin-15–producer colon carcinoma cells induce neoangiogenesis in the mucosa adjacent to the tumor [134]. The heterodimer IL-23, consisting of p40 (IL-2–like protein) and of the novel p19 protein (distantly related to IL-6, G-CSF, and IL-12 p35) exerted tumor-growth inhibition as expressed in murine colon carcinoma and melanoma cells, and rendered these hosts immune against challenge with tumor cells [135]. Replication-defective adenovirus Ad.mda-7 expressing IL-24, in combination with glutathione transferase treatment, synergistically suppressed the growth of kidney carcinoma cells by generating free radicals; N-acetyl cysteine, by neutralizing free radicals, abolished this effect [136]. Human mesothelioma cells transduced by Ad-IFN-␥, the E1E3-deleted replication-defective recombinant adenovirus type 5, delivering the IFN-␥ gene inserted into a plasmid and also containing a CMV promoter/enhancer and a SV40 polyadenylation signal, inhibited tumor cell growth in vitro and induced antitumor immune reactions in the nude mouse, consisting of NK cells and macrophages (see Parts I and III) [121,137–139]. VEGF production and survivin overexpression in mesothelioma cells could be suppressed effectively (see Part III). Are cytokines induced in xenografts by oncolytic viruses the same or different from those that arise in patients who are enrolled in a clinical trial with these viruses? Interleukin-18, the IFN-␥–inducing factor, is produced by osteoblasts and macrophages and acts through GM-CSF in inhibiting the multinucleation of osteoclasts. By upregulating osteoprotegerin (a TNF family member) and obilizing GMCSF–producing T cells, IL-18 antagonizes osteoclastogenesis. Interleukin-18 inhibited the lodging of multiple myeloma cells (see Part V) in the vertebrae of SCID mice through the activation of NK cells. With IL-12, it inhibited bone resorption by osteoclasts. Physiologically, IL-18 serves as an auto- and paracrine growth factor for osteoblasts, whereas M-CSF and IL-11 are osteoclast growth factors. If effective IL-18 inhibitors could be generated, would they suppress the growth of osteosarcoma

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cells? In mice bearing human MDA-231 osteolytic breast cancer cell xenografts, IL-18 inhibited osteolytic bone metastasis formation [140–147]. Therefore, if the xenografted host produces IL-18, osteoclasts will be suppressed, IFN-␥ will be produced, NK cells will be activated, and growth of the xenograft will be naturally inhibited. In multiple myeloma cells, FasL and Fas receptor co-expression may be upregulated, leading to self-destruction by apoptosis of the xenografted myeloma cells (see Part V). Interleukin-18 production by the xenografted host may invalidate an assay in which an agent is tested against a transplanted tumor. Matrix Metalloproteinases and Chemokines Matrix metalloproteinase-2 and MMP-9 (see Part II) stimulate VEGF release from ovarian carcinoma cells and batimastat (BB-94) inhibited this process. Endothelin or VEGF-producer ovarian carcinoma xenografts invaded the abdominal cavity and grew as ascitic tumors [148–150]. Matrix metalloproteinase-2 and MMP-14 promote melanoma cells to assume tubular formations referred to as ‘‘vascular mimicry’’ (see Part III). Antisense oligonucleotides directed at laminin and antibodies directed at MMP-2 and MMP-14 inhibited the process of vascular mimicry [65,151]. Gelatinolytic MMP-2 (gelatinase A) and MMP-9 (gelatinase B) promote the progression of uterine cervical carcinomas and liver metastases of colon carcinomas [152,153]. The production of macrophage migration inhibitory factor (MIF) is increased by lysophosphatidic acid [154]. Macrophage migration inhibitory factor promotes neoangiogenesis and tumor growth. Antisense-MIF plasmids and antibodies neutralizing MIF inhibited tumor (murine colon carcinoma) growth [155]. The Canadian preparation Virulizin derived from bovine bile (Lorus Therapeutics, Toronto) suppresses the growth of human tumor xenografts and stabilizes the disease in patients with advanced cancers. The mechanism of action is claimed to be macrophage activation [156]. Indeed, macrophages could be acting, as designed, against auto- or allogeneic foreign invaders, or yield to subversion and support the growth of autologous or transplanted tumors.


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Before modern technology (labeled monoclonal antibodies specific to the gene product protein) it was not easy to detect and titrate cytokines [157]. Macrophage migration inhibitory factor drives the growth of certain colon carcinoma cells and an antisense oligonucleotide directed at the mRNA of MIF inhibited the growth of these tumors. Furthermore, tumor-infiltrating macrophages secrete VEGF and induce neoangiogenesis in favor of the tumor [158–160]. Proinflammatory cytokines (TNF␣, IL1␤, and IL-6) block growth of breast carcinoma cells by inhibiting IGF-1–induced DNA synthesis [161,162]. Insulin growth factors and their receptors serve many tumors in the role of autocrine growth circuits. Ligand- or receptor-specific monoclonal antibodies, As-ODN (see Part III), or the mTORtargeting rapamycins could neutalize or switch off the signal cascade emanating from the ligand-bound IGF-R [163–171]. Are these growth factors readily available in the murine host for xenotransplanted human breast cancer cells? Stromal cell cultures deriving from rat lymph nodes could provide such growth factors (IGF-1 and EGF) for human breast cancer cell lines established in culture [46]. Desmoplastic reaction [172] to certain tumors (breast carcinoma, carcinoid, melanoma, pancreatic carcinoma) may be defensive or may be a host reaction promotional to tumor growth, which may be absent in xenotransplanted tumors. Chemokine receptor CXCR4 is activated by its ligand CXCL12 and the system is operational in metastatic melanoma. Tumor cell growth is promoted by interactions between melanoma cells and ␤1 integrins of endothelial cells. Other inflammatory chemokines (CCL3, CCl20) attract CD8 immune T cells and NK cells into a colon carcinoma tumor model. Expression of CCR7 chemokine receptor in esophageal carcinoma cells endows the tumor cells with increased invasiveness and metastatic potential. Human pancreatic cancer cells express the chemokine MCP-1/CCL2 and attract macrophages. High CCL2 levels and extensive macrophage invasion correlated with increased IFN-␥ and TNF-␣ production and increased the rate of apoptotic tumor cell deaths [173–176]. If stromal cells and macrophages of the xenograft-bearer host are not immediately subverted, they may not provide cell

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growth promoting MMPs and chemokines for the tumor. The tumor deprived of this support may experience increased vulnerability from noxious substances assayed against it. Mesothelioma Antisense Bcl-2/BclXL-directed interventions disable xenografted mesothelioma cells (see Part III). Mesotheliomas often contain SV40 genomic sequences (acquired from the first-generation polio vaccines?) [177], inactivate the wild-type p53 by deletion of p14, and activate the Wnt pathway. Antisense Bxcl2/BclXL-directed therapy disables xenografted mesothelioma cells (see Part III) [178–180]. The term Wnt stands for the derivatives of the Drosophila gene wingless and the mouse gene int; these two genes found fused are called wnt; they encode glycoprotein ligands that are cognate to the ‘‘fizzled’’ receptors. The Wnt pathway is essential in embryonic life; when it malfunctions, fruitflies emerge without wings or tadpoles grow two heads. The Wnt-related gene ‘‘dickkopf’’ directs development of the head and eyes (see Parts III and V). The Wnt pathway suppresses the enzyme glycogen synthetase kinase 3␤. This enzyme, when functional, eliminates ␤-catenin, the cadherin-associated protein, by ubiquitination and proteasomic degradation. Catenin mediates the linking of cadherin to the cytoskeleton. In mesothelioma cells, ␤-catenin is overexpressed and induces transcription of c-myc and cyclinD genes [181–184]. In addition to mesothelioma, Wnt is malfunctioning in melanoma cells, colonic polyps (APC; FAP), gastric adenomas, hepatocellular carcinoma, medulloblastoma, aggressive fibromatosis, and soft-tissue sarcomas [185,186]. In colonic polyps (APC), loss of APC protein liberates Wnt signal transduction, as ␤-catenin translocates into the nucleus and the downregulating effect of APC on COX-2 ceases to exist [186]. Cyclooxygenase-2 is active in colon carcinogenesis. The gene of fibroblast growth factor 18 (FGF18) is targeted by ␤catenin and is overexpressed in colon carcinoma cells, where it functions as a growth factor. The 23 FGF genes regulate organogenesis in embryonic life. Of EGF-R inhibitors (C225, Erbitux, Imclone, New York, NY; gefitinib, Iressa, AstraZen-


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eca; OSI-774, erlotinib, Tarceva, Genentech) (see Part I), ZD1839 suppressed EGF-mediated signaling in EGF-RⳭ mesothelioma cells (see Part III) [187] (Table 4). Catenins, Caveolins, Connexins The Sloan Kettering defective retrovirus possesses the oncogene v-ski. The human cellular homologue c-ski resides at 1p36 [184]. The SKI protein antagonizes TGF␤, inactivates the Rb pathway, and activates [1] Wnt/␤-catenin signaling, [2] the tissue-specific coactivator of the androgen receptor FHL2, which binds ␤-catenin and functions as a transcriptional repressor, and [3] the melanocyte master regulator MITF (microphthalmia-associated transcription factor) in melanoma cells. These activated pathways render an essential contribution, in addition to mutated RAS/MAPK and BRAF pathways (see Part I), to the maligancy of this tumor. In early stages of melanoma, there is cytoplasmic ␤-catenin but its expression is reduced in the advanced stage of superficial spreading melanoma [185]. The gene-targeting vectors ␤-cateninKO-neo and –hyg delete catenin exons II-IV from colon carcinoma cells with potential therapeutic valuue [188]. Co-activation of ␤catenin, c-myc, and PKC (see Parts II and III) downregulates caveolin-1 (Cav-1). Caveolae, the caveolin-coated cell surface invaginations, interact with lipid rafts, participate in endocytosis and molecular trafficking, emit signals, and exercise tumor suppressive functions, as cells in their terminally differentiated stage overexpress caveolins. Caveolin-1 inactivates H-Ras, Src kinases, G proteins, EGF-R, nitric oxide, and PKC. In the thyroid gland, caveolins act as tumor suppressors, and they are downregulated in follicular thyroid carcinoma [189–193]. Caveolin-1 expression is depleted in HPV-transformed squamous cells of the uterine cervix [194]. In the thyroid gland, caveolins act as tumor suppressors and are downregulated in follicular thyroid carcinoma [189]. In contrast, in hormone-resistant prostate cancer cells, Cav-1 is overexpressed and soluble Cav-1 stimulated the growth of prostate cancer cells [195]. The behavior of caveolins in xenografted tumors is not known. Do they retain their tumor-suppressive

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function, or are they switched to be subverted to function as tumor promoters? The connexin proteins form gap junction channels within the membranes of adjacent cells, allowing molecular trafficking. Connexin proteins are inhibitory to cell divisions and act as tumor suppressors; the connexin 43 gene (Cx43) is a recognized tumor-suppresor gene. Connexins are depleted in lung cancer and glioblastoma cells. Cessation of growth and loss of tumorigenicity was displayed by lung cancer cells transfected with Cx43 cDNA [196,197]. It is not known how connexins of xenografted human tumor cells relate to the heterologous stromal cells of their new host. Autocrine Circuits Tumor cell populations derive paracrine growth factors from their stroma (fibroblasts, endothelial cells, monocyte-macrophages, microglia cells) and manufacture their own growth factors in autocrine loops. Examples for this latter event abound. Among many others, these are G-CSF for transitional cell carcinoma of the urinary bladder [198], acetylcholine or bombesin for small-cell carcinoma of the lung [199], and erythropoietin (induced by hypoxia) for breast cancer cells [299,201]. The EBV-encoded small RNA (EBER) induces the production of IGF-I in gastric carcinoma cells, which also express IGF-IR and use the system as an autocrine growth loop [132]. Insulinlike growth factor and its receptor are highly promotional for tumor growth and targeted for therapy [202], but their behavior in xenografts is not well understood. When tumor cell populations are extricated from their natural environment, the subpopulation dependent on paracrine growth support is expected to perish; the subpopulation self-sustaining by autocrine growth loops would prevail. This latter tumor cell subpopulation is the one that is assayed in tissue cultures or in xenografts. The EGF homologue TGF␣ promotes tumor cell growth and invasiveness (colon carcinoma, glioma, melanoma). TGF␤ inhibits tumor cell growth but paracrine growth factor-independent tumor cells may gain resistance to it and some tumor cells (colon, breast, cholangiocarcinoma) may expropriate


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TGF␤ and its receptor for an autocrine growth loop [42,203,204]. The growth regulatory role of TGF␣␤ encompasses many tumor categories, from breast and ovarian carcinomas to brain and neuroectodermal tumors [203–208]. Tumor growth factor-␤ transactivates the VEGF gene in cholangiocarcinoma cells, whereas vascular endothelial cells in the tumor bed overexpress VEGF-R (see Part III) [209]. Tumor growth factor-␤ is an inhibitor of hepatocellular carcinoma cells; when it is switched off, the tumor cells produce VEGF and gain enhanced malignant potential [210]. TGF␤-R kinases are inhibited by SB431542; PDGF-R kinases are inhibited by AG1296, and c-Kit kinases are inhibited by imatinib (see Part I) in osteosarcoma cells that replicate in response to TGF␤ and PDGF [211–213]. The sensitive TGF␤ receptors are Alks; sphingosine-1 phosphate and AKT drive PDGR-R [213]. How do xenotransplanted human tumors set the balance of TGF␣␤ in their new host? Stromal cell-derived factor-1 (SDF-1) is produced in the bone marrow and is the cognate ligand of chemokine receptor CXCR4, which is expressed in B-lineage lymphocytes and CD34 hematopoietic progenitor (stem) cells. It stimulates formation of pseudopodia and cell migration, especially in lymphoid cells. It activates the anti-apoptotic NF␬B system [214]. The c-rel gene encodes the p50 and p65 subunits of the NF␬B heterodimer. The v-rel gene was discovered in the RevT reticuloendothelial retrovirus, inducer of bursal lymphomas in turkeys. NF-␬B is constitutively activated in Reed-Sternberg cells of Hodgkin’s disease and is under the promotional control of SDF-1 in multiple myeloma and in B-CLL cells, protecting these cells in collaboration with IL-6 from dexamethasone-induced apoptosis. The activation of NF-␬B in muliple myeloma cells can be inhibited by anti-CXCR4 monoclonal antibodies rendering the tumor cells vulnerable to pro-apoptotic stimuli (see Part V). Stromal cell-derived factor-1␣ (SDF-1; CXCL.12) is the ligand of chemokine receptor CXCR4 expressed on endothelial cells responding to angiogenic stimuli and on monocytes obeying chemotactic stimuli. Stromal cell-derived factor1 does not limit its stimulatory effect to B-lineage lymphoid cells; under its effect, breast cancer cells emit pseudopodia and

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migrate [215]. It protects from death explanted B-CLL cells and myeloid progenitor cells of the bone marrow [58,216]. PDGF secreted by tumor cells and endothelial cells stimulates the pericyte to release VEGF, which induces endothelial cells to form neovasculature in the tumor bed (see Part III). The distamycin analogue NSC651016 (Suradista, Pharmacia; Upjohn; Pharmitalia Milan, Italy) inhibits neoangiogenesis induced by CXCL.12. Suradista and its analogues (see Part III) exert an antitumor effect for xenografted tumors driven by bFGF, but without the toxicity of suramin[217,218]. Tannic acid in nontoxic concentrations inhibits CXCL.12 (the ligand) and suppresses the migration of monocytes and breast cancer cells [219]. Virus-Induced Cytokines and Chemokines Chemokine receptor CXCR4 serves as coreceptor with CD4 for the entry of HIV-1; some of the molecular inhibitors of HIV1 entry may also downregulate the NF␬B anti-apoptotic system in some human malignant tumors. Human immunodeficiency virus-1 protease inhibitors exert anti-angiogenic effects in KS (see Part III). Acquired immunodeficiency virus-associated KS cells are driven by SDF-1 of capillary endothelial cell origin. Stromal cell-derived factor-1, the ligand of receptor CXCR4, inhibits entry of HIV-1 into susceptible cells. Polyphemusin (from Limulus polyphemus) also interacts with CXCR4 in an inhibitory fashion regarding HIV-1 entry. The viral macrophage inflammatory protein (vMIP-II) encoded by the KS-associated HHV-8 prevents signal transduction from CXCR4. Viral macrophage inflammatory protein-I is the ligand of chemokine receptor CCR8, which is expressed on KS cells. Whereas IFN-␥ is listed as a growth factor for KS cells (see Part III), the IFN-␥–inducible chemokine protein (IP-10), vMIP-II, or SDF-1␣ inhibit signal transduction from KS cells’ G-protein-coupled receptors (GPCR) [220–225]. Human immunodeficiency virus-1–infected macrophages or primary effusion lymphoma cells (with or without HHV-8 co-infection) use NGF for an autocrine growth circuit [226,227]. Is there any connection between the NGF and SDF-1 to CXCR4 circuits


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and, if so, how is it altered in xenografts of KS cells? Alveolar rhabdomyosarcoma cells driven by the PAX3, 7/FKHR fusedgene product protein growth factor also overexpress CXCR4 and accept SDF-1 as a growth factor [228]; the CXCR4 inhibitor T140 blocks this growth circuit. Stromal cell-derived factor1 facilitates the formation of bone metastases by prostate cancer cells [229]. When we infect patients or xenografts of their tumors with genetically engineered or naturally oncolytic viruses, are chemokines induced in both situations the same or different? Some chemokines exert tumor survival-enhancing effects, whereas others are detrimental to the tumor. Viral infections induce proinflammatory cytokines: IFN␣ and TNF-␣ by NDV; and these with IFN-␤, IL-1␤, IL-6, IL10, MIP-1␣␤, MCP1, MCP3, and chemokines by influenza A virus (especially H5N1) [230,231]. Investigators of the Wellstat Biologics Corporation (Gaithersburg, MD)"desensitize’’ patients who experience ‘‘acute toxicity’’ upon the first i.v. inoculation of PV701 oncolytic NDV preparation [232]. Certainly, these virally induced proinflammatory cytokines, contrary to their expected antitumor effect, may, on occasion, promote the growth of some tumor cells so programmed, given that the use of defensive cytokines or chemokines in the autoor paracrine growth circuits of tumors is not uncommon. HORMONE-RELATED EVENTS IN BREAST AND PROSTATE CANCERS Complex Interactions Allo- and xenotransplantations for the transfer of organs or lympho- and hematopoietic cells are extensively studied as potential therapeutic interventions [233,234]. Allo-transplanted lymphoid cells at the price of graft-vs.-host reaction may exert graft-vs.-leukemia or even graft-vs.-tumor immune reactions [235]. For preclinical assays of therapeutic agents, including oncolytic viruses, human tumors are transplanted into athymic hairless (‘‘nude’’), SCID (severe combined immunodeficient), or X-irradiated mice. There appears to be a discrepancy between the results of these preclinical tests and those

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of Phase I and II clinical trials. Although complete eradications of xeno-transplanted human tumors frequently occur, complete clinical responses remain a rarity, the most common clinical response being stabilization of the disease and, less frequently, PR and MR. Androgen-dependent and independent prostate cancer xenotransplants responded equally well to the EGFR tyrosine kinase inhibitor ZD1839 (Iressa, Astra Zeneca) (see Part I) and exhibited increased susceptibility to bicalutamide, carboplatin, and paclitaxel. The polyphenolic flavonoid antioxidant silibinin/silymarin inhibited the growth of prostate cancer xenografts by neutralizing IGF through the upregulation of IGF-binding proteins. This substance is available as a dietary supplement and its consumption may lower PSA levels in patients with indolent prostatic carcinomas [236]. Quercetin inhibited Erb-2 and Erb-3 expression and antagonized TGF␣ and EGF-R signal transduction in, and thereby inhibited the proliferation of, prostate cancer cells [237]. Some Chinese herbal formulas contain substances that induce apoptosis in prostate cancer cells [238,239]. The isoflavonoid genistein and grape seed extract inhibit NF␬B and the AKT signaling pathway in cultured prostate cancer cells [240–242]. The growth of prostate cancer xenografts was inhibited by combined treatment of the hosts with 1␣,25-dihydroxyvitamin D3 and 9-cisretinoic acid [243]. Adenoviral insertion of the prolactin gene encoding the 16-kDa prolactin fragment into prostate cancer cells abolished xenograft formation of these tumor cells, presumably because of anti-angiogenic effects [244]. The apoptosis-inducing natural protein U19 is frequently underexpressed in prostate cancer cells because of loss of hetero- or homozygosity or hypermethylation of its gene; gene expression is testosterone-regulated and the gene product protein is proapoptotic [245]. The clinical use of the system remains unresolved. Ansamycin antibiotics, especially 17-demethoxygeldanamycin (17-AAG), are inhibitors of chaperone proteins of the Hsp90 family [246]. HER2-positive and androgen receptor (AR)-mutated prostate cancer xenografts were inhibited by 17AAG. Nonmutated AR tyrosine kinases can be phosphorylated


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within the pathways of other growth-factor receptors: HER2, EGF-R, IGF-R, and keratinocyte GF-R, and by IL-6. 17-Demethoxygeldanamycin interferes with these phosphorylation pathways (see Part III). Monoclonal antibody rhu␣VEGF inhibits the growth of several xenografted human tumors, among them the androgen-independent CWR22R prostate cancer cell line [247]. Certain prostate cancer cells express VEGF receptors for autoor paracrine growth stimulation. Further, the VEGF gene is transactivated by androgens; VEGF-producing cells upon abrupt withdrawal of androgen support may succumb to apoptosis. In contrast, both VEGF and PSA levels rise in patients harboring androgen-independent tumors. Human breast cancer xenografts did not grow or metastasize and are rejected consequentially to peritumoral or intraperitoneal injections of betaglycan, the soluble TGF␤III receptor that binds TGF␤ with high affinity [248]. In certain tumor cells, including those of pancreatic carcinoma, TGF␤ functions as an auto- or paracrine growth factor [249]. Some breast cancer cell lines developed at M. D. Anderson Hospital in the 1970s overexpress the fgfr genes encoding bFGF receptors; the MDA-MB-134 cell line is estrogen receptor positive and expresses elevated levels of fgfr-1 and fgfr-4 mRNAs because of an amplified fgfr-1 gene; however the ligands FGF-1 and FGF-2 inhibited the growth of these tumor cells even though the receptor FGF-R was functional [250]. Fibroblast growth factor-negative breast cancer cells transfected with fgf-1 or fgf2 genes induced neovascularization and gained a rapid growth rate [251]. The histone deacetylase inhibitor PXD101 suppresses the growth of human colon and ovarian carcinoma xenografts; it was also tested against breast cancer cells [252,253] because another histone deacetylase inhibitor suberoylanilide hydroxamide acid (HDAC SAHA) (see Part II) induced differentiation of human breast cancer cells. Breast cancer cells with ras mutation are resistant to radiotherapy because of constitutively overactive PI3K and AKT signaling. PI3K inhibitor LY294002 reverted radioresistance and restored radiosensitivity of this tumor [254]. This molecular mediator also is strongly pro-apoptotic in pancreatic carcinoma

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cells [255]. Constitutively active AKT pathway deprives breast cancer cells of their estrogen and tamoxifen sensitivity [256]. The new antiestrogen ICI182780 (fulvestrant, AstraZeneca) downregulates cyclin D, inhibits c-myc, and transfers the CDK inhibitory protein p21WAF/CIP (wild-type p53-activated fragment/cycline-dependent kinase-interacting protein) from cyclin D/cdk4 to the cyclin E/cdk2 complex, resulting in inceased levels of CDK inhibitor p27KIP1, which brings the cell to quiescence (Q ⳱ G0) [257–259]. Stromal cell-derived factor1 (vide supra) interacts with estrogen receptors and with estradiol in promoting breast cancer cell mitoses [259]. The PKC inhibitor staurosporine (see Part II) causes apoptotic death of human breast cancer cells [260]. The lectin galectin-3 is overexpressed on fibrosarcoma and on MDA-MB-435 breast carcinoma cells and facilitates metastatic spread; treatment of the xenograft-bearing host with a genetically engineered truncated form of galectin inhibited metastasis formation [261]. These estrogen-independent breast carcinoma cells overexpress Erb2/HER2 receptors and the c-jun and c-fos oncogenes, but respond to bombesin antagonists with cessation of growth [262,263]. Astonishing Observations Two recent articles review stromal cell and tumor cell interactions in prostate and breast cancers [264,265]. Carcinomaassociated fibroblasts promote malignant transformation of benign hypertrophic prostatic epithelial cells. Reactive fibromuscular stroma predicts recurrence-free survival of patients with prostatic carcinoma [266]. Reduced desmin and smooth muscle ␣-actin in the stroma were adverse, whereas high labeling indices for these markers in the stroma were very favorable prognostic predictors. Fibroblast growth factorR1 activation promoted and FGF-R2 activation inhibited the proliferation of prostatic carcinoma cells. Fibroblast growth factor-R1 signaling upregulated osteopontin, thereby enhancing anchorage-independent tumor cell invasiveness and VEGF overexpression; it downregulated the tumor-suppressive thrombospondin [267] (see Part III). Proteasomes prevailed throughout evolution from archaea (archebacteria) to the


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mammalian cell, where these structures degrade proteins, among them products of oncogenes (Myc) and those of tumorsuppressor genes (p53; PTN). The proteasome inhibitor bortezomib (PS-341, Velcade) (see Part V) induces apoptosis of androgen-dependent and -independent prostate cancer cell lines and xenografts thereof and synergizes with TNF␣ and TRAIL [268,269]. ERⳭ mammary gland fibroblasts expressing HGF, collagens, fibronectin, EGF, and IGF-1 promote the proliferation of mammary epithelial cells, but laminin exerts antiproliferative activity through ‘‘loss of estrogen responsiveness’’ [64,270,271]. Transgenes encoding ribozymes that specifically target the HGF gene or the Met (the receptor) gene, transduced by retroviral vector into HGF-producer stromal fibroblasts or into MET-expressing breast cancer cells, silenced this paracrine growth loop [272]. HER2/neu could be suppressed by R11577 (tipifarnib, Zarnestra, Janssen) (see Part I) and trastuzumab or by the monoclonal antibody 2C4 [262]. The rapamycin analogue CCI-779 (Wyett-Ayerst) [273], the inhibitor of mTOR and the AKT cascade, suppresses the growth of breast cancer xenografts and, in a clinical trial, it showed activity (PR inductions) against hormone- and chemotherapyrefractory breast cancer, serving as one of the examples of a xenograft assay correctly predicting subsequent clinical results. Heat shock proteins (Hsp 90) chaperone the estrogen receptor (and also promote AKT and Raf-1 proteins) [274]. The geldanamycin derivative 17AAG is an inhibitor of Hsp 90 by occupying the ATP-binding pocket of the chaperone. When ER loses its chaperone, it is condemned to degradation by proteasomes. The same fate awaits the Akt, Raf-1, IGF-R1, and erbB2 proteins after the loss of their Hsp 90 protection. Tamoxifen opposes 17AAG and preserves ER. Tamoxifen-resistant breast cancer cells still may be inhibited by other estrogenreceptor antagonists (ICI 164,384; ICI 182,780, fulvestrant), stimulating degradation of ER (Table 6). In addition, aromatase inhibitors suppress estrogen-2 synthesis. The luteinizing hormone-releasing hormone analogues (SB-75, Cetrorelix) imitate surgical oophorectomy. Not with tamoxifen, but in combination with fulvestrant, 17AAG may act additively in the treatment of estrogen-sensitive and refractory breast can-

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cers [275–277]. In other systems cited, normal fibroblasts could induce differentiation of basal cell carcinomas, urogenital sinus mesenchymal cells induced differentiation of transitional carcinoma cells of the urinary bladder, and human colon carcinoma cells underwent differentiation in the presence of fetal rat mesenchymal cells [264,265]. In the male fetus, the Mu¨llerian ducts regress under the effect of the Mu¨llerian inhibiting substance (MIS). In the feTable 6 Pathobiology of the Breast Cancer Cell and Its Repair HER2 (ErbB2/c-erbB2/HER2/neu): Its genes are mapped at 17q12–21. Its genes were discovered transduced by avian erythroblastosis retroviruses (c→ v-erb). HER2 is a member of the ErbB family: ErbB1, 2, 3, 4. Responds to ligands epidermal growth factor (EGF), transforming growth factor-alpha (TGF␣), amphiregulin, ␤-cellulin, epiregulins, heregulin (HRG␤)/ neuregulins. ?HER2 expression is equated with adverse prognosis and chemotherapy resistance. Trastuzumab (Herceptin, Genentech) downregulates HER2 expression and upregulates cyclin kinase inhibitor p27Kip1 and retinoblastoma (Rb) protein p130. The ↑HER2 ↑EGF-R expressing BCC converts the estrogen receptor (ER) competitive antagonist tamoxifen (TXF, Nolvadex) into agonist-stimulating breast cancer cell (BCC) mitosis. The ligands to EGF-R/HER2, EGF and HRG␤, signal cross-phosphorylation of the TXF-ligated ER, resulting in BCC mitosis-induction. Fulvestrant (Faslodex) retains its ER antagonism in HER2 EGF-R BCC. ZD1839 (gefitinib, Iressa) synergizes with fulvestrant in suppressing growth of HER2 EGF -R BCC stimulated by TXF1,2. In BCC with ER or downregulated insulinlike growth factor-I receptor (IGF -IR), fulvestrant resistance develops and BCC mitoses are resumed. HRG␤-stimulated HER2/EGF-R signaling through the anti-apoptotic AKT kinase pathway (inhibitory to pro-apoptotic BAD) counteracts gefitinib-mediated growth inhibition. Phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002 synergized with gefitinib in suppressing mitoses of TXF-resistant, HRG␤1-stimulated BCC. Insulinlike growth factor-IR phosphorylation by ligation of IGF-II cross-phosphorylates EGF-R signaling pathway, but EGF-R pathway phosphorylation does not cross-phosphorylate the IGF-IR pathway. AG1024 (Table 2) inhibits IGF-IIR, but leaves EGF-R signaling unaffected. TXF-resistant BCCs overexpress IGF-II but not IGF-I3,4,5. ↑HER2-specific immune T cells are cytotoxic to HER2 autologous BCC6. HER2/neu oncoprotein is antigenic and induces immune reactions to BCC when used as a vaccine7. (Continued)


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Table 6 Continued Letrozole (Femara, Novartis) extends relapse-free survival of TXF-naïve and TXF-pretreated patients8. Dual inhibition of EGF-R/HER2 by GW572016 suppresses growth of even trastuzumab-resistant BCC in vitro9. Farnesyltransferase inhibitor R115777 synergized with TXF; flavopiridol synergized with epothilone in suppressing growth and inducing apoptosis of BCC10 (Table 2). Although erythropoietin receptor (EpoR) is overexpressed in some BCC (Part IV) and it activates signal transducers and activators of transcription (STAT) (Figures 1 and 2) and nuclear factor kappa B (NF␬B), thus exerting cell-survival and antiapoptotic effects; it does not enable BCC to resist chemotherapy.11 Receptors for adeno-associated viral (AAV) vectors are expressed on BCC and AAV vectors are very good candidates for viro- and gene therapy for these (and other—glioblastoma) tumors.12 AdEHT2 and Ad-CMV-CD are used for virotherapy (Table 1). 1 Baylor College of Medicine, Houston, TX; AstraZeneca, Maclesfield; Imperial College of Science, Technology and Medicine, London, United Kingdom. 2 Kawasaki Medical School, Kurshiki, Okayama, Japan. 3,4,5 Tenovus Centre for Cancer Research, Cardiff; City Hospital Nottingham; AstraZeneca, Alderley Edge; United Kingdom. 6 Technical University of Munich, Bavaria, Germany. 7 GlaxoSmithKline Biologicals, Rixensart, Belgium; Ringshospitalet, Herlev Hospital, Aalborg Hospital, Odense University Hospital, Pharmexa A/S, Denmark; Leiden University Medical Center, The Netherlands; Hammersmith Hospital, Leicester Royal Infirmary, London, United Kingdom. 8 Ringshospitalet, Denmark; Chinese Academy of Medical Sciences, Beijing, China; Petrov Research Institute of Oncology, St. Petersburg, Russia; Hospital Universitario de la Princesa, Madrid, Spain; CHG Andre Boulloche, Mondbeliard, France; Novartis Pharma AG, Basel, Switzerland. 9 University of California, Los Angeles, CA; GlaxoSmithKline, Research Triangle Park, NC. 10 Institute for Cancer Research; Royal Marsden Hospital, London, United Kingdom; Johnson & Johnson, Titusville, NJ; H. L. Moffitt Cancer Center, University of South Florida, Tampa, FL. 11 Molecular Radiation Biology Lab, University Clinic Freiburg, Germany. 12 Haukeland Hospital, Bergen, Norway; National Institutes of Health, Bethesda, MD; University of Washington, Seattle, WA; University of Pennsylvania, Philadelphia, PA.

Table 6. Condensed and selected summaries of lectures and abstracts of the San Antonio Breast Cancer Symposia, 25th (2002) and 26th (2003), Lippman, Marc E., editor; printed in Breast Cancer Research and Treatment 2002; Supplement, volume 76 and 2003; Supplement, volume 82.

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male fetus, the coelomic epithelium invaginates to form anlagen from which the uterus and the upper vagina develop. Highly purified recombinant MIS inhibited the growth of human ovarian carcinoma cell lines xenografted into immunosuppressed mice [278]. Intratumoral injection of the liposome-encapsulated proapoptotic virally encoded protein E1A of adenovirus type 5 (see Part I) into xenografted HER2/neu-positive breast adeno- and head and neck squamous cell carcinomas resulted in tumor regressions. Phase I clinical trials confirm apoptosis induction of injected breast, ovarian, and squamous cell carcinomas, but without curative effect. Small molecular inhibitors and monoclonal antibodies compete for targeting the EGF-R in breast (and other) cancer cells [279–284]. These modalities of treatment will eventually be given in combined protocols (Table 5). MISCELLANEOUS AGENTS TESTED IN XENOGRAFTS Xenografts of Human Tumors Are Very Sensitive to Noxious and Natural Substances The mushroom toxin illudin contains the DNA alkylating agent irofulven (MGI-114), which completely destroys human cancer xenografts in nude mice. In clinical trials, only occasional PR occurred (one in a patient with pancreatic carcinoma) but stabilization of disease was more common, but renal and hematologic toxicities (thrombocytopenia) disallowed dose escalation. Subsequent French studies indicated unique cytotoxicity of irofulven to cancers of epithelial cell origin (squamous cell carcinoma of the head and neck; hormone-refractory prostatic carcinoma and others) (285, 286). K-ras mutation in pancreatic cancer cells activates the anti-apoptotic transcription factor NK␬B. The endogenous polypeptide NF␬B inhibitor is degraded by proteasomes. Proteasome inhibitors sustain the downregulation of NF␬B, allowing apoptosis to ensue when induced. The proteasome inhibitor PS-341 (see Part V) suppressed the growth of orthotopically xenografted pancreatic carcinomas because of caspase activation and DNA fragmenta-


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tion; further extensive necrosis of the microvessel network occurred [287,288]. This compound is active against xenografted colon, head and neck, lung and prostatic carcinomas. The proteasome inhibitor PS-341 induces Bcl-2 phosphorylation and cleavage, depriving NSCLC cells of their anti-apoptotic machinery. Another NF␬B suppressor is the vitamin E analogue ␣-tocopheryl succinate; it sensitizes lymhoma cells to TRAILinduced apoptosis [289]. Leukotriene B4 stimulates, but its receptor antagonist LY293111 inhibits, the growth of pancreatic cancer xenografts by abrogating ERK1 and ERK2 phosphorylation [255]. The benzimidazole derivative mebendazole (Vermox, McNeil, Ft. Washington, PA) induced apoptotic death of xenotransplanted lung cancer cells and suppressed neoangiogenesis within the xerotransplants [290,291]. The somatostatin analogue RC-160 and the luteinizing hormone-releasing hormone agonist SB-75 ([D-Trp6]-LH-RH) inhibited the growth of human pancreatic cancer xenografts in nude mice [292]. Interferon␣ and gemcitabine acted additively against orthotopically implanted human pancreatic carcinoma xenografts in nude mice; endothelial cells of the tumor bed died with apoptosis [293]. Both NCLS and, more frequently, SCLC express neuropeptide receptors and utilize bradykinin as their para- or autocrine growth factor. The bradykinin antagonist CU201 suppressed the growth and induced apoptosis in cultures or in xenografts of these cancer cells, and acted additively or synergistically with chemotherapeutical or biological agents (paclitaxel; ZD1839). Bradykinin under physiological conditions induces IL-12 production by DCs with subsequent Th1 immune reaction to follow. It was previously known that the nonapeptide bradykinin contributed to the development of endotoxin shock and that bradykinin antagonists (angiotensin-II; B2 receptor antagonists) ameliorated the outcome of endotoxin shock [294–297]. Now the bradykinin antagonist CU201 (B9870) emerges as the strongest inhibitor of lung cancer cells that exhibit neuroendocrine features. This compound acts additively or synergistically with chemotherapeuticals (vinorelbine, etoposide, cisplatin, paclitaxel) and with the EGF-R TKI ZD1839 (gefitinib; Iressa) [294]. The diterpene glycoside cotylenin A of plant origin induces differen-

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tiation of human leukemic cells (AML, acute promyelocytic leukemia). In combination with IFN-␣, cotylenin induced the DR5 gene encoding the receptor for TRAIL in lung cancer cells. In xenografts, lung cancer cells underwent programmed cell death, whereas normal lung epithelial cells were spared [298]. In the endoplasmic reticulum, the Ca2Ⳮ-ATPase pathway is inhibited by thapsigargin (THG); from mitochondria, THG liberates pro-apoptotic proteins that activate caspases, leading to cell death through DNA fragmentation. In the machinery of apoptosis, pro-apoptotic proteins, the cytoplasmic-to-mitochondria BAX, and the mitochondrial Bak are antagonized by anti-apoptotic proteins Bcl-2 and BclXL.When THG acts, Bid is cleaved and Bax initiates the cascade, beginning with the release of cytochrome C from mitochondria and leading through caspase activation to programmed cell death. A chemically modified form of THG (L12ADT) is coupled with a peptide that is a substrate of the protease PSA, which hydrolyses the prodrug to release THG in prostatic tissues; there, THG/ L12ADT induces apoptosis and when it was tested against human prostate cancer xenografts, THG/L12ADT retarded the growth of these tumors [299,300]. This mechanism of THGinduced death may result in a clinical trial for prostate and colon carcinomas at the H. L. Moffitt Cancer Center in Tampa, FL. Flavonoids (see Part II), such as favopiridol, genistein, or quercetin, are pro-apoptotic in cancer cells; the benzopyronhydroxyphenyl phenoxodiol shows intensive activity in human breast, prostate, and ovarian cancer cells. It induces apoptosis in chemotherapy-resistant ovarian carcinoma cells by inhibiting the X-linked inhibitor of apoptosis (XIAP), liberating FLICE (caspase 9) by eliminating its inhibitory protein FLIP, and thereby activating the intrinsic pathway to apoptosis. The PI3K/Akt pathway is anti-apoptotic because it activates NF␬B and inactivates by phosphorylation BAD, the Bcl-2 antagonist of cell death, and suppresses caspase 9 and FasL [301]. Phenoxodiol, by antagonizing the translocation of Akt into the nucleus, reduces the high levels of FLIP and liberates the extrinsic Fas-mediated apoptotic pathway through caspase 8. Ovarian carcinoma xenografts regress in the hosts treated


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with phenoxodiol [302]; the Yale University School of Medicine is enlisting patients with chemotherapy-resistant ovarian carcinoma for a clinical trial with phenoxodiol. The combination of HA14-1 and PK11195 (see Parts I and II) inhibits Bcl-2, induces translocation of Bax to mitochondria and antagonizes the peripheral benzodiazepine receptor (PBR) of mitochondria, resulting in cytochrome C release for the initiation of the apoptotic cascade [303]. The PBR agonist Ro5-4864 antagonizes PK11195 but pan-caspase inhibitors (z-VAD-fmk) fail to counteract HA14-1. This combination of apoptosis inducers awaits clinical trial at the Hunstman Cancer Institue in Salt Lake City, UT. The pentacyclic triterpenoid of the cyclosqualenoid family, ursolic acid, inactivates the anti-apoptotic NF␬B and consequentially suppresses the expression of cyclin D, COX-2, and MMP-9, rendering tumor cells chemotherapysensitive [304]. It may be tested for such efficacy in a clinical trial at the M. D. Anderson Cancer Center in Houston, TX. The anti-angiogenic agent squalamine passed its preclinical assys and is being tested in Phase I clinical trials [305]. The COX-2 inhibitor NS398 acts as an antiproliferative and proapoptotic agent in hepatocellular and head and neck squamous cell carcinomas [306,307]. Murine NK cell-depleted SCID mice accept i.v. injected human melanoma xenografts that grow as lung metastases. Purified human NK cells from healthy donors given i.v. with IL-2 and IL-12 eradicated these metastases [308]. Immune T cells (as tumor-infiltrating lymphocytes) and lymphokineactivated killer cells (LAK) are in clinical use at the National Cancer Institute and elsewhere [309,310]. Although the xenograft may be subdued by the injected cytotoxic lymphocytes, in the tumor-bearing natural host, suppresssor T cell clones may arise for the protection of the tumor [311,312]. Helper T cells may overcome the suppressor T cell clone [313].). Soluble viral peptides may induce immune tolerance [314]. If a nonpathogenic oncolytic virus induces immune tolerance toward itself, the oncolytic process could advance unimpeded, with lack of virus-neutralizing antibodies. These events may or may not be reproducible in a xenograft.

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Endless List of Anti-Tumor Agents and Interventions Interleukin-4 receptors are overexpressed in pancreatic and breast carcinoma cells. Pseudomonas exotoxin fused with IL4 forms a chimeric protein attached to and endocytosed by the receptor. By intraperitoneal and intratumoral injections, the IL-4 cytotoxin eradicated 60% of xenografted human pancreatic carcinomas and reduced the growth of breast carcinoma xenografts. It induced macrophage and neutrophil leukocyte infiltrations into the regressing tumors. Its deleterious actions against normal IL-4 receptor-expressing cells is unknown. Because malignant glioma cells constitutively overexpress the receptor for IL-13, these cells readily accept attachment of the cytotoxin consisting of the fused proteins of IL-13 and Pseudomonas exotoxin; because of apoptotic death of the tumor cells, even established tumors regress [315–317] (see Part V). Xenografted arginine succinate synthetase-deficient arginine auxotrophic human melanoma cells do not grow in pegylated arginine deaminase-treated animals [318]. The dithiocarbamate disulfiram (DSF) left melanocytes intact but activated the apoptotic pathway in cultured melanoma cells. N-acetyl-cysteine (NAC) reversed the inhibitor of ␥-glutamylcysteine synthetase, and buthionine sulfoximide (BSO) augmented this effect. Dithiocarbamate disulfiram combined with cisplatin or nitrosoureas awaits clinical trials [319]. The tryphostin AG1024 inhibits IGF-R; in human melanoma cells it inhibits the MAPK/ERK pathway and restores tumor-suppressive Rb function [320,321]. Accordingly, the IGF-R system of colon carcinoma cells is similarly targeted [202]. The chloroindolyl sulfonamide cell-cycle inhibitor E7070 arrests the cell at G1→S, upregulates p53, and releases apoptotic pathways in colon carcinoma cells. In a Phase I clinical trial it induced long stabilization of disease in patients with advanced cancers [322]. Ecteinascidin-743 (ET-743, Yondelis; PharmaMar, Madrid, Spain) (see Part III) from the Caribbean tunicate Ecteinascidia turbinata inhibits nucleotide excision repair and downregulates the P-gp MDR-1 gene product protein by forming


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covalent guanine adducts as it attaches to the minor groove of DNA. It can overcome multidrug resistance. In xenografted breast carcinoma cells, it synergized with paclitaxel; in Ewing’s sarcoma cells it induced massive apoptosis [323–325]. Dexamethasone protected rats against ET hepatotoxicity [326]. Naamidine, an alkaloid from the sponge Leucetta, targets the extracellular signal-regulated kinases ERK1 and ERK2; it is antimitogenic in human squamous carcinoma cells [327]. The tunicate Aplidium albicans from the Mediterranean sea yields the depsipeptide didemnin, aplidine; it cleaves the protein Bid, the connector of extrinsic (CD95 Fas-mediated) and intrinsic (mitochondrial) apoptosis in human leukemic cells (see Part III) [328]. Epigallocatechin-3-gallate induces, in human head and neck squamous carcinoma cells, a drop of cyclin D1 and rise of p21Cip1 and p27Kip1; a reduction of hyperphosphorylated Rb, resulting in G1 arrest of the cell cycle [320,329]; a decrease of Bcl-2 and BclXL and increase in Bax proteins; inhibition of EGF-R, STAT, and ERK phosphorylation; and inhibition of TGF␣-induced stimulation of the c-fos proto-oncogene. It synergized with 5-fluorouracil. Statins are 3-hydroxy-3-methylglutaryl CoA reductase inhibitors synthesized and licensed for the treatment of hypercholesterolemia. In malignant tumors, these compounds show anti-invasive, antiproliferative, pro-apoptotic, and radiosensitizing efficacy [330]. The Princess Margaret Hospital in Toronto, Canada, tests statins in combination with chemo-biotherapeuticals for antineoplastic efficacy. The cardiac glycoside bufadienolide (hellebrin) induces mitochondrial apoptosis preferentially in malignant T (Jurkat) cells, and overexpression of Bcl-2 or the administration of the pan-caspase inhibitor z-Vad-fmk antagonized this effect [331,332]. Many new TKIs (see Parts I-II) have passed through preclinical assays and are in Phase I or Phase II clinical trials. The major targets of these TKI are the EGF-R from sarcomas [187] to lung cancer [333–335] (see Part I); CI-1033 for Erb2 [336]; PTK787/ZK222584 (PTK/ZK) for VEGF-R [337]; PKI166; CI1033 for HER2/neu [338–340]; and wortmannin for PI3K [341]. The pan-erbB-R inhibitor CI-1033 irreversibly blocks signal transduction from the receptor in chemotherapy-

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resistant breast cancer cells [336]. The water-soluble quinazoline CI-1033 (Pfizer) binds irreversibly to EGF-R tyrosine kinase and is a pan-erbB2-4 inhibitor. It inhibited the growth of human carcinoma cell lines in vitro and eradicated human cancer xenografts [342]. In clinical trials, it induced only one PR but many cases of stabilizations of metastatic disease (once in a case of osteosarcoma). The pyrollo-pyrimidine derivative PKT-166 (Novartis) [343], a reversible inhibitor of EGF-R, is performing well against xenografted human cancers; in nude mice it inhibited the growth of orthotopically xenografted human pancreatic carcinoma cells and reduced VEGF and bFGF production in the xenograft. No remissions were induced in a Phase I clinical trial involving 44 patients with metastatic cancers. Against xenografted kidney carcinoma, the drug performed best when it was given in combination with gemcitabine [344]. However, the combination of somatostatin analogue RC160, luteinizing hormone-releasing hormone antagonist Cetrorelix, and bombesin antagonist RC-3940-II acts on xenografted kidney carcinoma cells by reducing EGF-R expression in the tumor cells and reducing growth hormone and IGF levels in the host, resulting in tumor regression [345]. The quinazolamine derivative GW2016 (Glaxo SmithKline, Brentford, UK) inhibits signal transduction from EGF-R and HER2/Erb/B2. In nude mice, the growth of squamous cell carcinomas was inhibited. Tumor cells pretreated with the drug failed to grow in xenografts [346]. OSI-774 (Tarceva, OSI Pharmaceuticals) (see Part I) in combination with a PI3K inhibitor (wortmannin) (see Part II) inhibited the growth of, and induced apoptosis in, xenografted human pancreatic carcinoma cells [340]. The drug that appears to recognize in vitro a difference between adeno- and squamous cell carcinomas in the heterogeneous group of NSCLC is ubenimex (Bestatin). It is more effective against squamous than adenocarcinoma cells [347–349]. In large clinical trials, it significantly prolonged 5 years disease-free and overall survival of patients whose primary squamous cell carcinomas of the lung were completely resected: 81% vs. 74% and 71.6% vs. 62% in treated vs. control patients, respectively [348,349].


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PART V: CLINICAL EXAMPLES: MULTIPLE MYELOMA AND GLIOBLASTOMA MULTIFORME MULTIPLE MYELOMA Pathogenesis Despite high-dose chemotherapy (melphalan 140 mg/m2 with, or 200 mg/m2 without total body radiotherapy given after four courses of the VAD regimen) consisting of vincristine adriamycin and dexamethasone and hematopoietic stem-cell rescue, either autologous or allogeneic, this disease remains incurable, although survival with subclinical disease is prolonged [1–5]. Even double high-dose chemotherapy with stem-cell rescue, at the risk of death consequentially to treatment morbidity, fails to promise cure, but definitely prolongs survival up to 42% at the seventh year. Patients who failed to achieve a CR at the first treatment benefited most from the second hematopoietic stem-cell rescue. Allogeneic lymphoid cells (NK cells), at the risk of morbidity and mortality, given after nonmyeloablative pretreatment, could induce PR and CR (‘‘graftvs.-myeloma’’ reaction) at a high rate. However, multiple myeloma (MM) is responding to biological interventions and is targeted for many modalities of biological therapy, including viral (genetically engineered measles virus; naturally oncolytic reovirus) agents [6]. Will viral agents match the efficacy


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of these biological interventions and is there a good rationale to combine virotherapy with some of the biological treatment modalities? Monoclonal gammopathy of uncertain significance (MGUS) with karyotypic instability may progress to MM. There are seemingly chaotic and promiscuous translocations of chromosomal segments in MM cells—less in the natural tumor than what is found in its established human myeloma cell lines (HMCL). The most common translocations involve cyclin D1 (11q13) and cyclin D3 (6p21) genes; the MM nuclear SET domain gene (4p16) and the FGF receptor 3 (FGF-R3) gene (der 14); and the c-maf genes (16q23; 20q11) (vide infra). The t(11;14)(q13;q32) translocation dysregulates cyclin D1, albeit at different break points, both in MM and in mantle cell lymphoma. The translocation t(4;14)(p16.3;q32.3) dysregulates the SET nuclear protein and the FGF-R3 genes. Translocation t(11;14) associated with ectopic expression of the FGFR3 gene occurs in 20% of MGUS plasma cells, in 50% in MM cells, and in 70% in HMCL. Next to the FGF-R3 gene is the locus of the transforming acidic coiled coil-containing gene (TACC3), which is normally active during embryonic life, falls silent, but becomes re-amplified in malignantly transformed cells [7,8]. The t(14;16)(q32;q23) translocation liberates the cmaf proto-oncogene encoding a transcription factor for IL-6. This oncogene was discovered in the avian retrovirus AS42. This retrovirus induces musculoaponeurotic fibrosarcomas in chicken and carries v-maf fused with the viral gag gene, but originally derives from c-maf. Next to the c-maf gene lies the tumor suppressor gene WWOX/FOR (16q23), encoding an oxidoreductase, but suffering a monoallelic inactivation in the translocation process. Translocations t(6;14)(p21;q32) dysregulates cyclin D3. [9,10]. Although no single mutation characterizes myelomagenesis, N-ras or K-ras mutations occur in about 50% of the cases. Patients with constitutively active N-ras mutation are resistant to doxorubicin and dexamethasone. Physiological activation of the Ras pathway by IL-6 is transient and the cell remains sensitive to doxorubicin. Microarray technology could distinguish four to six groups of MM patients stratified accord-

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ing to gene mutations and stromal cell and IL-6 dependence, given that some mutations render the MM cell independent from paracrine growth factors, including IL-6 [11,12]. Translocations of c-myc: t(8;14), such as in Burkitt’s lymphoma, or Bcl-2: t(14:18), such as in follicular lymphoma, seldom occur in MM. Deletions occur in 13q14ⳮ, resulting in monoallelic loss of the Rb gene (13q14). Its nuclear phosphoprotein suppresses the cell cycle at G1→S; Pⳮ pRB is active and arrests the cell cycle; PⳭ pRb is inactive and lets the cell cycle continue. Multiple myeloma cells express PⳭ pRb or deletion (monoallelic loss) of the Rb gene. Cycline D kinase inhibitors (p15, 16, 18INK4A) are lost through deletions. Mutations of K-ras and N-ras (codons 12, 13, 61) occur in fewer than or up to 5% in MGUS and in 40% in MM cells (especially after culture in vitro). Regarding p53 and its sequence-specific DNA-binding protein, it is mutated in HMCL frequently, but seldom in native MM cells. The PTEN gene (vide infra) encoding a pro-apoptotic phosphatase counteracting the anti-apoptotic Akt system, is lost in MM cells [13,14]. Although telomerase is active in MM cells, adding TTAGGG repeats to chromosomal ends, the telomeres are unusually short (perhaps because plasma cells are terminally differentiated). The importance of telomerase activity in oncogenesis was documented when SV40 and H-ras genomic sequences and those of the ribonucleoprotein telomerase were combined to create malignant cells in vitro [15]. Telomerase inhibitors; the Gquadruplex intercalating tetramethyl-4-pyridyl porphyrin chloride; and the thiophosphoramidate oligonucleotide, which raises levels of p21 and phosphorylated p53 for apoptosis induction, are in clinical trials (vide infra) [16–18]. Interleukin-6 protects MM cells against dexamethasoneinduced apoptosis. Wild-type Rb suppresses IL-6 production, whereas IL-6 shifts Rb from Pⳮ to PⳭ form. Hyaluronic acid produced by stromal cells promotes IL-6 binding to its receptors IL-6R␣ and gp130. The subunit gp130 accepts as its ligand IL-6, IL-11, ciliary neurotrophic factor, cardiolipin, oncostatin M and leukemia inhibitory factor. It activates through the Janus family tyrosine kinases STAT1 and STAT3 (Figure 4). In normal B-lineage lymphocytes, IL-6R can be downregu-


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Figure 4 Interleukin-6 activates STAT3, which in turn transactivates the BCL2 gene for overproduction of the anti-apoptotic Bcl-2 protein. The myeloma cell thus gains resistance to programmed cell death (apoptosis). (Courtesy of Professor Richard Jove Ph.D. of the University of South Florida, H.L. Moffitt Cancer Center, Tampa, FL.)

lated, but in MM cells, IL-6R remains permanently overexpressed. Although IL-6 can function as an autocrine growth factor in MM cells, it frequently is provided to MM cells as a paracrine growth factor by stromal cells, together with VEGF, IL-1␤, IL-10, TNF␣, TGF␤, MMP-1, osteoprotegerin OPG-Ractivator of NF␬B (RANKL), macrophage (M⌽) inflammatory protein 1␣ (MIF), FGF, IGF, and HGF. Statins (coenzyme A inhibitor cholesterol-lowering agents lovastatin, pravastatin) inhibit the growth of human myeloma cells, but IL-6 antagonizes this effect [19–24]. Human IL-6R does not accept mouse IL-6, so xenografted MM cells are deprived of the growth-promoting effect of paracrine IL-6 and become more vulnerable to pro-apoptotic insults that MM cells existing in their natural

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microenvironment could withstand. There is no evidence that HHV-8–infected stromal cells provide paracrine IL-6 to MM cells. The multinucleated giant osteoclast differentiates from monocyte-M␾ stem cells. TH2 helper CD4 lymphocytes produce the pleiotropic immunomodulatory cytokine IL-4, which primarily stimulates the proliferation of B-lineage lymphocytes. Other sources of IL-4 production are mast cells and eosinophil leukocytes (as in the stroma of Reed-Sternberg cells). In order to act, IL-4 binds either one of its receptors—IL-4R␣␥ or IL-4R␣/IL-13R␣1. Signaling from these receptors runs through the Janus kinases and involves both insulin receptor substance (IRS) and STAT activation. STAT6 suppresses mRNA for RANK (the RANKL receptor). In response, B cells produce immunoglobulins (first IgE). The effects of IL-4 on osteoclast precursors are suppressive. RANKL, the TNF realeted ligand, and IL-4 are antagonists. Whereas RANK emits signals to activate NF␬B, IL-4 suppresses this pathway. In osteoclasts, the IRS pathway and cell differentiation are inhibited by IL-4 because IL-4 suppresses the expression of RANK, the receptor, in immature osteoclasts. Under the effects of IL4, even fully mature osteoclasts stop resorbing bone. Thus, IL4 deprives osteoclasts of stimulation by RANKL to mature and differentiate. Even the M-CSF pathway, another stimulator of osteoclastogenesis, is suppressed by IL-4 [25]. Here, wellknown proto-oncogenes interact. Proto-oncogene c-fms (locus at 5q21-32) was transduced by the McDonough strain of the feline sarcoma retrovirus (v-fms), encoding a transmembrane glycoprotein receptor for the ligand M-CSF. Proto-oncogene cfos (locus at 14q21-22) was transduced by the Finkel-BiskisReally (FBR) mouse osteosarcoma retrovirus (v-fos). The gene product protein c-Fos transactivates nuclear genes, which dictate terminal differentiation of monocytes-M␾. The c-KitⳭ, cFmsⳭ, c-FosⳭ, RANKⳮ stem cell gives rise to DCs under the effects of GM-CSF, which acts as a suppressor to osteoclastogenesis, whereas TNF␣; M-CSF; and, later, RANKL promote osteoclastogenesis from the same stem cell. Receptor activation of NF␬B (RANK) is expressed by osteoclasts; the cognate receptor activator of NK␬B ligand (mRANKL⇒sRANKL) de-


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rives from osteoblasts, stromal cells, and malignant (MM) plasma cells. Osteoprotegerin (OPG), a member of the TNFR family, acts as a soluble decoy receptor for binding RANKL and, by depleting the supply of the ligand, it protects against osteolysis. Apoptosis of myeloma cells induced by TRAIL/ Apo21 (TNF-related apoptosis-inducing ligand) was averted by OPG, therefore exerting a tumor-protective effect. Bone resorption markers are the tartrate-resistant acid phosphatase and bone collagen degradation products; bone alkaline phosphatase and osteocalcin are markers for new bone formation. Additional osteoclast-activating ligands are IL1, IL-6, and TNF␣ deriving from the myeloma cell or its stroma. The osteoclastogenesis inhibitory factor (OCIF), a member of the TNF family, is identical to OPG: Both bind RANKL. Osteoprotegerin plasma or serum levels are decreased in patients with clinically active MM, but the technology (enzyme-linked immunosorbent assay; ELISA) for titrating the levels of this substance is very difficult; for example, in patients with colorectal or pancreatic carcinomas, higher than normal OPG levels were measured. TRAIL is also depleted by its binding to the decoy receptor OCIF/OPG. Removal of RANKL favors the host by suppressing osteolysis by the osteoclast; removal of TRAIL favors the myeloma cell by eliminating the events leading to its programmed cell death. Receptors for TRAIL are complex: DR4 and DR5 transmit signals leading to apoptosis; DcR1 and DcR2 are decoy receptors that capture TRAIL, but remain silent. The two-faced OPG, the recombinant human rhOCIF (Sankyo, Tokyo, Japan), and a RANK-HuTgG fusion protein (RANK-Fc) are in clinical trials [26–33]. The Wnt-related (see Part III & IV) dickkopf (‘‘fathead’’) gene product protein DKK1 is an inhibitor of osteoblast differentiation and activity. The gene is reactivated in myeloma cells; DKK1 levels are high in the bone marrow and in the blood. High DKK1 levels correlate with the development of lytic bone lesions caused by the loss of osteoblast activitites that are inhibitory to osteaclasts and reparatory to osteolysis [34]. In summary, myeloma cells and stromal cells produce RANKL and thus promote osteoclastogenesis. Production of

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the RANKL antagonist OPG is downregulated. The Wnt antagonist DKK1 blocks osteoblast differentiation and is overproduced by myeloma cells. Undifferentiated osteoblasts also secrete large amounts of RANKL. Plasma cells in MGUS syndrome do not (as yet) produce DKK1. Patients with far-advanced MM and bone lesions show decreased DKK1 blood levels, inasmuch as overactivated osteoclasts can downregulate DKK1 output. However, the molecular mediator of the therapeutic value with which osteoclasts suppress DKK1 production has not as yet been isolated and identified. Interleukin-18, the IFN-␥–inducing factor, is of osteoblast or M␾ origin (see Part IV). It suppresses osteoclast maturation not by IFN-␥, but by GM-CSF induction from subclones of T lymphocytes or from osteoblasts. Interleukin-18 is related to IL-1 and IL-12 and synergizes with IL-12 in inducing IFN␥ secretion from T cell subclones. Mature osteoclasts express the IL-18 receptor MyD88; IL-18 inhibits the bone-resorbing activity of mature osteoclasts. When IL-18 induces IFN-␥, it will suppress osteoblasts [35–41]. In a human myelo-monocytic cell line (KG-1 cells) that expresses Fas, the receptor, IL18 induced Fas ligand co-expression and upregulated the p53 protein. These events drive KG-1 cells to die apoptotoic deaths [39]. It is presumed that such events could also occur in myeloma cells exposed to IL-18. Proteasome antagonists of NF␬B activation (P341; vide infra) protect against bone resorption. The bisphosphonates are licensed products for the same purpose [42]. Bisphosphonates are in use to treat lytic-destructive bone metastases of patients with breast cancer or blastic bone metastases of patients with prostate cancer. In the latter entity, Osteoprotegerin/osteoclastogenesis inhibitory factor (OPG/OCIF) emerges as a potential therapeutic agent [27]. The CD95 Fas receptor gene may undergo mutations in MM cells. Multiple myeloma cells attached to fibronectin in their native environment mobilize high FLIP levels and thereby gain protection against nonmutated Fas receptor-mediated apoptotic death induced by doxorubicin and alkylator chemotherapeutic agents, whereas suspended MM cells taken out of their microenvironment exhibit low FLIP levels and become defenseless against apoptosis induction. In their micro-


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environment, protection of MM cells against apoptotic death is mediated by ␤1 integrins; antagonists of this substance exist and are readied for clinical trials [43]. Human MM cells injected intravenously into SCID mice cannot lodge in the bone marrow in animals treated with IL-18 (IFN-␥–inducing agent) because of NK cell activation [44]. In evaluating the results of clinical trials, the natural history of MM should be considered. Patients without chromosome 13 deletion, low ␤2 microglobulin and high p27Kip1 cyclin/ CDK complex-inhibitor levels without anemia or hypercalcemia and with normal kidney function at presentation respond better to treatment and live longer; their life expectancy is from 48 to 80 months. Patients with monoallelic loss of 13q, t(4; 14) or t(14;16) involving the IgH gene (14q32) and low p27Kip1 levels usually live only from 16 to 25 months [45]. Biotherapy The catalytic proteinase enzyme system referred to as proteasomes is being targeted for cancer therapy [46]. The ubiquitinproteasome proteolytic system removes mutant, damaged, and misfolded proteins from the cytoplasm. When the proteasome system is inhibited in a tumor cell, however, the cell activates an apoptotic pathway. In MM cells, the proteasome inhibitor PS-341 overcomes the anti-apoptotic effect of IL-6; phosphorylates the p53 protein on Ser15 (a process inhibited by caffeine); degrades MDM2, the p53 antagonist; inhibits TNF␣-induced NF␬B activation; switches off DNA repair by cleaving certain phosphatidyl inositol kinases; activates caspases 3 and 8; and inhibits paracrine growth factor release from bone marrow stromal cells. Multiple myeloma cells so afflicted die apoptotic deaths. Further, PS-341 attacks and phosphorylates the gene product protein Bcl-2, especially when bcl-2 is translocated: t(14;18), as in certain lymphoma cells. The phosphorylated Bcl-2 protein is condemned to proteolytic cleavage, resulting in the arrest of the cell cycle in G2-M and apoptotic cell death (for illustration see cited references). Other agents that phosphorylate and thereby inactivate Bcl-2 are the phosphatase inhibitor okadaic acid, the PKC-inhibitor bryostatin (see Part II),IL-3, and Vinca alkaloids). The dipeptide Phe-Leu pyrazyl-

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carbonyl boronate 20S proteasome-inhibitor PS-341 (bortezomib, Velcade, Millennium Pharmaceuticals), in its first trial, induced one CR in nine heavily pretreated MM patients and reduced the paraprotein levels in others, while restoring other immunoglobulin levels, but also inducing maculopapular skin rash. One heavily pretreated patient with mantle cell lymphoma experienced PR [47]. In a later trial of 54 MM patients, the response rate, including significant reduction of paraprotein levels, was 85% (ASH, Orlando, FL, 2003). Bortezomib was tested in hundreds of MM patients (heavily preatreated patients in the SUMMIT trial, with 20% response rate; and minimally pretreated patients in the CREST trial, with 30% response rate). Its approval was based on the APEX trial, in which it induced 3% CR and 25% PR; with stabilization of disease, response rate rose to over 90%. Malaise with nausea and diarrhea, peripheral neuropathy, anemia, and thrombocytopenia are adverse side effects, involving 50% of the patients [48–52]. Bortezomib-resistant MM cells remain sensitive to CDDO-imidazolide treatment. This compound also eliminates IL-6–producing stromal cells and synergizes with bortezomib. Interleukin-6 or dexamethasone could not block CDDO-Im–induced apoptosis of MM cells. The pan caspase inhibitor z-VAD-fmk protected MM cells from bortezomib- and CDDO-Im–induced apoptosis. The licensed Velcade (Millenium) was included in the Physicians’ Desk Reference in 2004 (pp 2136–2139). The next targets of bortezomib are CLL [53] and some solid tumors (including prostatic and NSCLC) because it exerts pro-apoptotic effects on these tumor cells in vitro or in xenografts [54,55]. Bone marrow endothelial cells proliferate in patients with MM [56,57]. Thalidomide (see Part III), the inhibitor of neoangiogenesis and TNF␣-induced NF␬B activation, elicited 32% clinical response in MM patients who were refractory to conventional therapy. Patients with elevated bFGF blood levels respond to thalidomide [58–61]. The DTPACE chemotherapy regimen works additively with thalidomide [62]. Thalidomide analogues, the immunomodulatory drugs (IMiDs), are more effective because of stimulation of IFN-␥, IL-2, and MM cellspecific immune T cell clonal expansion and NK cell prolifera-


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tion [63,64]. CC-5013 (Revimid, Celgene) induces a significant drop of paraprotein levels in 63% of relapsed MM patients; if leukopenia occurs, G-CSF (filgrastim, Neupogen, Amgen) restores white blood cell count. Neovastat (Æ-941, AEterna Laboratories, Quebec, Canada) inhibits MMPs and neoangiogenesis by suppressing bFGF and VEGF, and its as-yet-uncompleted Phase II trial shows paraprotein level reductions in MM patients [65]. S3APG (S-3 amino-phthalimido-glutarimide) inhibits both MM and Burkitt’s lymphoma cells and is awaiting Phase I and Phase II clinical trials. Multiple myeloma cells express VEGFR-1 and VEGF stimulates their growth. Multiple myeloma cells also secrete VEGF for autocrine growth loop and for IL6 induction in the bone marrow stromal cells [66]. The VEGFR tyrosine kinase inhibitor PTK787/ ZK222584 antagonized the growth of MM cells even in co-cultures with bone marrow stromal cells [67]. Combretastatin-A4 (CA4P) (see Part III) arrests the cell cycle in G1-M and inhibits microtubule assembly in B-CLL cells, which die in a ‘‘mitotic catastrophe’’ [68]. It is awaiting clinical trials for B-lineage malignancies. The cycline-dependent kinase inhibitor flavopiridol (see Part II) suppressed Mcl-1 overexpression and induced apoptosis in MM and B-CLL cells; it is in clinical trials [69]. The GAG glycosaminoglycans (syndecan-1 heparan; neoglycan) may inhibit cell growth (hyaluronic acid for melanoma cells) or stimulate cell growth (hyaluronic acid for MM cells). The carbodimide-modified GAG neoglycan inhibited MM cell growth. Rapamycin analogue CCI-779 suppressed the growth of PTEN-deficient myeloma cells. Phosphatase on chromosome ten (PTEN) functions in a tumor-suppressor system by inactivating the PI3K/Akt pathway, which is liberated and is constitutively operational in myeloma cells [70]. However, PTENdeficient myeloma cells are sensitive to mTOR (mammalian target of rapamycin) inhibition. Rapamycin synergized with dexamethasone in apoptosis induction in myeloma cells [71]. Inhibitors of constitutively active STAT pathway exist and are piceatannol, a stilbene from Euphorbia, and the synthetic tyrphostin AG490. They abolish the exemption from apoptosis and restore chemotherapy sensitivity of MM cells [72].

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Apoptosis induction in MM cells by arsenic trioxide (As2O3) is intensified by coadminstration of ascorbic acid and buthionine sulfoximide, which reduces glutathione levels [73,74]. Alemtuzumab (Campath-1H) reacting with CD52 could attack myeloma cells and could induce C’- or ADCC-mediated tumor cell lysis [75]. Some myeloma cells express low levels of HER2 [76]. CD20Ⳮ MM cells usually are of the small mature plasma cell morphology, but suffered translocations t(11;14), have 13qⳮ, and breaks at 14q32. These patients may respond to rituximab (Rituxan, Biogen Idec, San Diego, CA) or trastuzumab (Herceptin, Genentech), respectively [77]. The chaperone molecule, heat shock protein Hsp90, blocks apoptotic protease activity of factor-1 (APAF-1) and promotes cell survival. Geldanamycin (GA) attaches to the ATPbinding pocket of Hsp90 and inactivates it. Defenseless MM cells succumb to apoptotic death. The 17-demethoxygeldanamycin (17-AAG) is in Phase I trials [78]. The histone deacetylase inhibitors (see Part II) FR901228 depsipeptide and SAHA are apoptosis inducers in MM cells and are in preclinical trials [79,80]. 2-Methoxyestradiol (2ME2, Panzem, Tetrionics, Madison, WI) is anti-angiogenic, causes G2-M arrest of the cell cycle in dexamethasone-resistant MM cells, and counteracts the anti-apoptotic effects of IL-6. It also upregulates the extrinsic pathway of apoptosis induction. In SCID mouse xenografts, it inhibited MM cell growth by 40%, including that of primary plasma cells taken directly from patients. Inhibited MM cells died apoptotic deaths. The 14-dehydro-2-ME2 analogue is 10 times more potent than the parental compound [81,83]. The TNF-related apoptosis-inducing TRAIL/Apo21 ligand elicits apoptotic cascade in MM cells; the protein-synthesis inhibitor cycloheximide and the PKC-inhibitor bisindolylmaleinimide restore MM cell sensitivity to TRAIL/Apo21 ligand [28]. Some proteins attach to membranes to function, but membrane attachment requires prenylation. Such lipid modification of these proteins—that is, addition of isoprenoid moieties to cystein-containing motifs at the C-terminus of these proteins—is carried out by the enzymes FT and geranylgeranyl transferase (GGT). The Rho family of Ras-related GTP-binding proteins and the Ras family proteins (see Part I) need gera-


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nylgeranylation and farnesylation, respectively, for their operational activities within the cell [84,85]. Geranylgeranyl transferase and FT carry out the tasks of prenylation. In myeloma cells, the pro-apoptotic molecular mediators BAX and BAD are neutralized by the formation of their heterodimers with the anti-apoptotic molecular mediators Bcl-2, BclXL, and Mcl-1 [86–89]. The latter emerges as the most important antiapoptotic molecular mediator mobilized for survival in MM cells. The mevalonate enzyme inhibitor lovastatin, the product of Aspergillus terreus, which is licensed to lower cholesterol, is pro-apoptotic for myeloma cells because it downregulates Mcl-1 expression and leaves Bcl-2 expression unaffected [19,20]. The GGT inhibitor GGTI-298 and the FT inhibitor FTI-277 (Calbiochem, Schwallbach, Germany) further inhibit prenylation and reduce Mcl-1 levels, driving myeloma cells to apoptotic deaths. Expression of Mcl-1 in myeloma cells also could be antagonized with As-ODN (see Part III). Lovastatin is pro-apoptotic in some other (AML, lung adenocarcinoma) cells. Farnyl transferase inhibitors SCH66335 and R115777 are in clinical trials in many tumor categories (see Part I), including MM. The latter, R115777 (tipifarnib, Zarnestra, Johnson & Johnson, Raritan, NJ), frequently (60%) stabilizes the disease, with reduction of the monoclonal protein levels. When tipifarnib inhibits phosphorylation of Akt, the PI3K/Akt pathway is interrupted, pro-caspase 3 cleavage occurs, and apoptotic death of the myeloma cell ensues. Farnyl transferase inhibitors show early favorable clinical results in the treatment of acute and chronic myelogenous leukemias and the myelodysplasia syndromes [89]. Rising to the ranks of effective inducers of apoptotic death in myeloma cells are the histone deacetylasae inhibitors (SAHA, depsipeptide) [79,80] (see Part II) and the peroxisome proliferator-activated ␥ receptor agonists (PPAR␥) (see Part I) ciglitazone and rosiglitazone. These agents are in clinical trials for MM and for Waldenstrom’s macroglobulinemia [90]. Chemotherapy resistance of tumor cells, including myeloma cells, consists of the efflux or extrusion of the drugs from the cell mediated by drug-transport glycoproteins (P-gp) or multidrug-resistance protein pumps (MDR-1). Another mech-

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anism of chemotherapy resistance entails the plugging of pores in the nuclear membrane, blocking access of the drugs to chromosomal DNA. Breast cancer resistance protein (BCRP) and lung cancer resistance protein (LCRP) accomplish these tasks [91–93]. All of these mechanisms are functional in myeloma cells. Levels of P-gp rise after chemotherapy with the VAD regimen, but MDR-1 expression remains low. Expression of BCRP is much lower than that of LCRP. The IL-2 antagonist cyclosporin, the product of the fungus Beauveria nivea, and its derivatives modulate P-gp and MDR gene expression. PSC833 (valspodar) inhibited P-gp in healthy liver and kidney cells as well, exposing these cells to excessive drug toxicity; it also caused cerebellar ataxia. Although the efforts to antagonize the drug-resistance pathways remain unattainable, apoptosis induction in myeloma cells with or without chemotherapy has been achieved. The anti-NF␬B PS-341 and As2O3, the JAK/ STAT inhibitor AG490, and the Bcl-2 inhibitor As-ODN (see Part III) appear to be the most promising interventions. The de novo (not chemotherapy-induced) phenomenon of cell adhesion-mediated drug resistance is mediated by the contact between ␣4␤1 integrin of myeloma cells and fibronectin of matrix cells. This contact activates NF␬B in the myeloma cell and induces IL-6 secretion from the stromal cell. PS-341 (bortezomib, Velcade) exerts anti-adhesive effect between myeloma and stromal cells and suppresses IL-6 production by stromal cells. SDF-1␣ is neoangiogenic and growth-supportive for myeloma cells. It can be inhibited by NSC65016 (Suradista) and by specific antibodies [94,95] (see Part IV). By the way, integrin ␣5␤1 serves as the entry site for parvovirus B19 [96]. The South American tree Tabebuia yields ␤-lapachone, a DNA repair inhibitor and inducer of cell death in many human tumor cells, including those of MM [63,64]. Of antisense oligonucleotides [97], the anti–Bcl-2 ODN G3139 (Genasense, Genta, Berkeley Heights, NJ) and the telomerase hTERT inhibitors are in Phase I through Phase III clinical trials (see Part III). The oligonucleotide thiophosphoramidate GRN163 targets the RNA of the human telomerase (see Part IV) functioning as a template antagonist; myeloma cells suffering telomere loss enter ‘‘crisis’’ and die [17,18].


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These As-ODN (see Part III) enhance the antilymphoma efficacy of rituximab, especially in EBVⳭ lymphoproliferative diseases [98] (Medical Education Resources Inc., www. uemeded.com/event 727669677424). Polymorphic epithelial mucin MUC1-expressing MM cells elicit the rise of HLA-I–restricted autologous immune T cell clones [99]; these T cells expanded in vitro may be used for adoptive immunotherapy. The autologous myeloma-follicular lymphoma idiotype globulin proteins are tumor-specific neoantigens eliciting antibody- and immune T cell-mediated reactions against tumor cells expressing these antigens. Multiple myleoma and lymphoma vaccines, including idiotype antigenpulsed DCs, coadministered with immunological adjuvants such as keyhole limpet hemocyanin (KLH) as a carrier for GMCSF (sargramostim, Leukine, Immunex, Kenilworth, NJ) induce molecular CR or maintain PR→CR induced by chemotherapy (MyVax姟, Genitope, Redwood City, CA; http:// www.genitope.com/myvax.html). CD6 T cell-depleted hematopoietic allografts from histocompatible donors elicit graft-vs.myeloma reactions in patients who received high-dose chemotherapy. The incidence of grade ⱖ2 graft-vs.-host disease is 17% and transplant-related mortality is 5%, but the CR rate is 28% and PR rate, 57%. The reduced-intensity conditioning regimens are administered before allotransplantation and aimed at facilitating acceptance of the allotransplant and its graft-vs.-tumor reaction at the price of a graft-vs.-host disease of varying severity, but with the reward of 65% CR or PR. Chimerism with donor cells occurs, yet 35% of patients relapsed (ASCO 噛2345 2003). Graft-vs.-myeloma–reacting lymphocytes are present before donor lymphocyte infusions and are CD3Ⳮ, CD8Ⳮ, and CD4ⳮ immune T cells. They expand after donor lymphocyte infusion and differ from the T cell clone responsible for graft-vs.-host disease [100]. In patients with MGUS advancing to MM, the invariant V␣24ⳭV␤11Ⳮ NKT cells lose their ability to produce IFN-␥ under the effect of glycolipids released by the plasma cells, or by their subverted stroma; these NKT cells normally respond to glycolipid ligands (CD1d) or can be activated by a synthetic ligand, ␣-galactosyl

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ceramide (␣-GalCer) [101]. Would ␣-GalCer prevent the MGUS→MM transition? GLIOBLASTOMA MULTIFORME Pathogenesis In the human brain, there are 10 times more glia cells than neurons. Although glia cells are electrically inexcitable, they are far from being silent: There is active communication among glia cells and between glia cells and neurons. There are myelinating glia cells (oligodendrocytes in the brain and Schwann cells in peripheral nerves) and protoplasmic and fibrillary astrocytic glia cells, providers of neurotrophic molecular mediators in the brain.Microglia is considered to be a defensive, inflammatory, and phagocytic faculty [102]. Glioblastoma multiforme (GBM) is a heavily vascularized, highly malignant tumor with more than 99% mortality despite surgery, radiotherapy, and chemotherapy (carmustine and cisplatin; temozolomide and 13-cis-retinoic acid; irinotecan, etc.) [103–105]. Tumor cells show limited susceptibility to irradiation, nitrosoureas, vincristine, procarbazine, and temozolomide (especially with 6qⳮ and 10qⳮ chromosomal deletions). However, arsenic trioxide (As2O3) induces acidic vesicular organelle (AVO) formation in GBM cells, resulting in autodigestion (autophagy or programmed cell death type II). The autophagy inhibitor bafilomycin A1 inhibits AVO formation and contributes to the type I caspase-mediated apoptosis [106]. Clinical trials with bafilomycin should begin at Mount Sinai School of Medicine, New York, NY, and elsewhere. Glioblastoma multiforme tumor cells express amplified or mutated EGF-R and PDGF-R, and a truncated EGF-R is constitutively autophosphorylated in some GBM cells. The PI3K/Akt cascade is overactivated. Overexpressed EGF-RvIII predicts poor survival. In de novo-arising primary GBM, EGFR is overexpressed and genes for INK4a and p14ARF proteins are deleted. In secondary GBM, evolving from another preexisting brain tumor, p53 is mutated or deleted and PDGF


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and its receptor are overexpressed. Genes coding for proteins of the p53 pathway are TP53, p14ARF, and MDM2. Genes coding for proteins of the Rb pathway are RB1, CDKN2A/B, and CDK4. Both lines may suffer mutations and deletions in GBM. Tumor suppressor genes for p14ARF (p53 pathway) or p15INK4ab (9p21) (Rb pathway) are silenced by hypermethylation in some brain tumors. Gene losses characterize the arising tumors: 1p36 and 19q13 leads to oligodendroglioma; 17p13, astrocytoma; 10ⳮ, high-grade glioma. Signal transduction from EGFR in GBM cells could not be completely suppressed by ZD1839 (Iressa) or the anilinoquinazole PD153035 (see Part I): PI3K/ Akt and MAPK/Erk remained active, whereas the same dosage of these inhibitors suppressed EGF-R of squamous carcinoma cells [107–117]. Hypoxic tumors overproduce the DNA-binding heterodimers HIF-1␣ and HIF-1␤. Hypoxia-induced factor-1␣ recognizes the genomic sequence of the hypoxia-responsive element 5′-RCGTG-3′. Hypoxia-inducible factor -1␣ is ubiquitinated and surrendered to proteasomal degradation by the VHL protein, except when the gene encoding this protein is mutated or deleted. The nuclear coactivator CBP/p300 interacts with HIF-1␣ and an asparagine hydroxylase mediates the HIF-1␣ and CBP/p300 relationship. Phosphatidyl inositol 3′ kinase and Akt promote HIF-1␣, whereas PTEN gene product protein would suppress it, were it not that this tumor-suppressor gene is often mutated in GBM cells. The PTEN gene (locus at 10q23.3) suppresses hyaluronic acid-induced MMP-9 expression in GBM cells. Loss of heterozygosity at chromosome 10q11-23 results in the deficiency of the gene(s) that upregulates the gene at 11p13 encoding the PAX6 protein, which is a DNA-binding transcription factor very active in embryonic life (directing development of the eye). Matrix metalloproteinase-9 is more active in primary than in secondary GBM. The notorious PI3K/Akt pathway can be inhibited by quercetin and its derivative LY294002; the fungal metabolite wortmannin; the Akt inhibitors (Calbiochem); and rapamycins, the macrolide antibiotics from Streptomyces hygroscopicus. In colon and prostatic carcinoma cells, PGE2 induces HIF-1␣→VEGF production. Wortmannin, rapamycin (Sigma), and the c-src inhib-

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itor PP2 (Calbiochem) inhibit this reaction. Hypoxia also induces the HIF1␣→VEGF reaction in these tumors [118–126] (Figure 5). Glioblastoma multiforme cells suffer early p53 gene mutation or the balance of proteins MDM2 and p14ARF favors MDM2 because the gene for the p53 protector p14ARF is frequently deleted [123,124]. Patients do not produce autoantibodies to the p53 protein [127]. Mutations of p53 correlate with EGF-R amplification in GBM cells, but without explicit growth advantage. In contrast, IGF-binding protein-2 overexpression enhances glioblastoma cell invasivesness caused by MMP-2 gene transcription and MMP-2 overproduction [128]. The aggregate response culminates in the massive overproduction of VEGF and other neoangiogenic growth factors (bFGF), hepatocytes, and scatter growth factors (HGF/SF), when c-met encoding the HGF/SF receptor is co-expressed for an autocrine growth circuit. A decoy HGF/SF molecule, NK4, can antagonize this growth loop and inhibits growth rate of GBM cells [129]. Glioblastoma multiforme cells downregulate the expression of the melanoma differentiation-associated 7 protein, a relative of IL-24, which is encoded by the gene mda-7. Such deficiency occurs in many other malignant tumors (breast, prostate, and gastrointestinal tract carcinomas). In mda-7–deficient cells, the antiapoptotic Bcl-2 and BclXL dominate over pro-apoptotic factors (BAX; BAK). When the genetically engineered adenovirus Ad.mda-7 reinserts the gene, however, the pro-apoptotic elements gain the upper hand and the tumor cell succumbs to programmed death [130]. The STAT3 inhibitor AG490 downregulates Bcl-2, BclXL, and Mcl-1 in GBM cells [131], offering itself to a combined protocol with Ad.mda-7 (not yet initiated). Peculiarly, GBM cells also express the neoangiogenesis inhibitor endostatin, the COOH terminal globular domain of collagene XVIII [132]; perhaps this is one reason why metatstases of GBM do not grow. Endostatin given intramuscularly suppressed the growth of some brain tumors [133]. Glioblastoma multiforme is the prototype of neoangiogenesis-inducing tumors: It transactivates the hTERT mRNA in the vascular endothelial cells of the tumor’s microenvironment (see Part


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Figure 5 Promoters and inhibitors of cell growth interact in a glioblastoma cell. Hypoxia-inducible factor 1␤ (HIF-1␤) acts prominently, unless it is degraded by ubiquitination (a favorable event). MDM2 and p53 compete; preserved p53 would remain pro-apoptotic, unless it is surrendered to the proteasome (an unfavorable event). If MDM2 is digested in the proteasome, the tumor cell may remain vulnerable to apoptotic death. PTEN is disabled by mutation and the PI3K/Akt pathway remains open unopposed. Two major overexpressed receptors (EGF-R; PDGF-R) constitutively emit promitotic signals. (Courtesy of Drs. Daniel J. Brat and Timothy B. Mapstone, Emory University Hospital, Atlanta, GA. Reprinted with the publisher’s permission from the Annals of Internal Medicine 2003; 138: 659–668.)

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IV). VEGF121, 165 isoforms contribute to vascularization and oxygenation of H-ras–mutated anaplastic astrocytic tumors, but do not promote their transformation into GBM, whereas tumors transfected by retrovirus expressing VEGF isoform genes grew faster, to a large size, and became hypervascular [134]. Tumor necrosis factor-␣ fulfills a proneo-angiogenic role in GBM [135]. Angiopoietin-2 is overexpressed by GBM cells. Angiopoietin-1 binds endothelial cell receptor Tie-2 and stabilizes established vasculature. Angiopoietin-2 inhibits Ang-1 binding by occupying the same receptor and thereby activating MMP-2 production by the tumor cell (see Part III). Matrix metalloproteinase-2–producing GBM cells gain enhanced invasiveness [136]. Further, GBM cells suck in excess sodium through inward sodium ion conductance channels because intracellular syntaxin 1A supplies are downregulated; GBM cells therefore change their shape and plasticity, enabling them to invade. Of those protein kinases of the C class that activate or inhibit sodium conductance through the ion channels, only the activator kinases are operational in GBM cells [120]. The INK4␣-ARF tumor suppressor locus encodes two proteins– p16INK4a and p14ARF –that modulate Rb/p53; these genomic sequences are often deleted in GBM cells. Exons 19-22 of Rb2/130 may remain intact, yet diabled Rb1 pathway and loss of PTEN predict brief survival [137,138]. Cyclin-dependent kinase inhibitor p27 is often downregulated by the overactive PI3K/Akt cascade in GBM cells, whereas genes for CDK4 and CDK6 are amplified. Overactive Ki-67 provides for accelerated G1→S progression. The PTEN (phosphatase and tensin homologue deleted from chromosome ten) gene is often mutated in, or is deleted from, GBM cells. Wild PTEN/MMAC is antineo-angiogenic, whereas constitutively overactive EGFR is proneo-angiogenic. Mutated or deleted PTEN on 10q23 and amplified or mutated EGF-R cooperate in transactivating the VEGF promoters via the PI3K/Akt pathway: Glioblastoma multiforme cells express increased levels of VEGF mRNA; LY294002 counteracts this deficiency [139–142]. Cyclooxygenase-2 and TNF␣ function as additional neo-angiogenic factors in GBM [135]. The chicken retrovirus CT10 harbors the onco-


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gene v-crk, which derives from its cellular counterpart c-crk. The gene product protein CrkI is overexpressed in GBM cells, where it induces the PI3K/Akt cascade and promotes invasiveness by rendering GBM cells free of cell-to-cell contact [143]. The avian sarcoma retrovirus UR2 yielded the v-ros protooncogene [144]; c-ros encodes a 260-kDa glycoprotein transmembrane receptor for an as-yet-unknown ligand. In some glioblastoma cells, consequentially to a microdeletion on 6q21, Ros is fused with the FIG protein, which is functional in the Golgi apparatus and forms the FIG-ROS fusion oncoprotein [145]. The signaling pathway of the constitutively active fusion oncoprotein is unknown, but Ros signaling normally is aimed toward phospholipase C␥ and the insulin-receptor substrates (IRS). In GBM cells arising de novo, the EGF-R gene is mutated, the receptor is truncated, and the result is EGF-R␯III. It is without its extracellular domain, so it is ligand-independent and is constitutively activated [107]. In secondarily progressing GBM arising from lower grade astrocytomas, the EGF-R is not mutated, but is amplified. In these tumors, p53 is deleted or mutated. Matrix metalloproteinase-9 expression is high (69% to 83%) in de novo tumors and low (14%) in secondary tumors [146,147]. The cascade EGF-R→Ras→MAPK/PI3K/ Akt leads to resistance to irradiation and chemotherapy. Mitogen-activated protein kinase overactivity and overexpression of MAPK-related proteins PKC (see Part II) and phospholipase C correlated with rapid tumor growth. Peculiarly, the nitrosourea BCNU may inhibit XRt-induced apoptosis and vice versa. XRt may inhibit BCNU-induced apoptosis [115]. The EGF-R inhibitor AG1478, the PI3K inhibitor LY29400, and the MAPK-1 inhibitor PD98059 (from Cell Signaling Technologies, Beverly, MA), may restore chemo-radiotherapy susceptibility of GBM cells in vitro. The FTI R115777 or SCH66336, blocking the Ras pathway (see Part I), reverse resistance of GBM cells to ionizing radiation [116,117,148–150]. Glioblastoma multiform cells lacking EGF-R␯III cells are less, whereas EGF-R␯IIIⳭ GBM cells are more, sensitive to chemo-radiotherapy. The mutant EGF-R␯III is common in native de novoarising GBM cells but is lost in established cultures of these

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cells [115,116]. Experiments with transgenic mice indicate that fibrillary astrocytomas grow in H-ras transgenic mice; oligodendrogliomas grow in H-ras and EGF-RvIII doubletransgenic mice, whereas EGF-RvIII alone did not induce gliomagenesis [151]. Platelet-derived factors A, B, C, and D attach to PDGF-R; GBM cells expressing both receptors and their cognate ligands expropriated the system for an autocrine growth loop. The piperazinyl quinazoline PDGF-R inhibitor CT52923 abolishes autophosphorylation of the receptor kinases and may retard growth of GBM cells in vitro [110,113]. Tissue factor pathway inhibitor-2 (TFPI-2) is encoded by its gene on 7q22; phorbols (PMA), diacyl glycerols (DAG), IFN-␣, and IFN-␥ activate the gene. The serine protease inhibitor TFPI-2 maintains the integrity of the extracellular matrix; it is underexpressed in GBM, contributing to the invasiveness of the tumor, but when the TFPI-2 gene is reactivated, it suppresses tumor cell invasiveness [152]. Nerve growth factor suppresses the growth of rat gliomas and induces differentiation of neuroblastoma, pheochromocytoma, and some glioma cells [153]. But its role in human GBM is not known. Human immunodeficiency virus-1–infected macrophages and AIDS-associated Kaposi’s sarcoma cells overexpress its receptor, p140trkA, and overproduce the ligand, but die apoptotic death when antibodies neutralize the ligand NGF [154]. Viral etiology for GBM is not proven; polyoma viral genomic sequences (SV40 from the first batches of the original live polio vaccines?) are found only occasionally in GBM cells and there is an absence of activated endogenous or exogenous retroviral agents in GBM tumors. However, refined genetic analysis of GBM cells (like those applied for Kaposi’s sarcoma cells) should continue. The ret→Ret proto-oncogene receptor captures glial cell-derived neurotrophic factor, active on neuroblastoma cells, and is inhibited by the pyrazolo-pyrimidine PP1; its activity in GBM cells is suspected. Germline mutations of ret are associated with multiple endocrine neoplasia (see cartoon in reference) [155,156]. Of the chemokines overexpressed by GBM cells, LARC (liver and activation regulated chemokine) stands out,


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whereas in normal brain cells there is no LARC mRNA activity. This chemokine attracts host CD4, CD8, and CD45RO lymphocytes into the tumor; it is however, unknown whether these lymphocytes attack and kill GBM cells or vice versa Glioblastoma multiforme cells may be armed with FasL and kill the lymphocytes [157]. The chemokine receptor CXCR4 is activated by its ligand CXCL12 or SDF-1 [158]. Glioblastoma multiforme cells produce and respond to SDF-1 through activation of ERK and PI3K/Akt pathways. Inhibitors of the system (antisense oligonucleotide against the receptor, antibodies against the ligand or receptor, or monoclonal antibody 12G5 against the receptor and LY294002 against PI3K) abolished GBM cell growth [159]. Glioblastoma multiforme cells produce SDF-1 and MCP-1, but it is unknown whether this is a host defense reaction or whether monocytes subverted by the GBM cells provide paracrine growth factors for the tumor cells. Monocyte chemoattractant protein -1 is one of the angiogenic chemokines, the receptors [regulated activation normal T cell expressed and secreted (RANTES), CXCR2, CXCR4) of which are expressed on endothelial cells and on many parenchymal and tumor cells. Matrix metalloproteinase-9 is also overexpressed in GBM tumors. The gene product protein PTEN would suppress its production if it were available in GBM cells (it is deleted from GBM and many other tumor cells) [160]. Matrix metalloproteinases-2 and MMP-9 are overexpressed in GBM cells and in the matrix of the tumor [161,162]. The serine protease urokinase-type plasminogen activator (uPA) and its receptor (uPAR) are overexpressd in GBM cells and are inhibited by phenylbutyrate or the peptide A6 or by an AS-ODN (vide infra) [139]. In the natural history of GBM, it is important to recognize the rare long survivors, who exhibit 19qⳮ; the function of the deleted chromosomal sequence is not known. Although it is not tested for, this chromosomal change may explain 10 years’ survival in subtotally resected Grade III and IV supratentorial astrocytomas. Short survivors have chromosomal deletions—6qⳮ, 10pⳮ, and 10qⳮ —and chromosomal gains—19pⳭ/qⳭ and 20qⳭ. Microarray analysis encompassing 12,000 genes relates better to subtype and prognosis

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than standard histological classification (163—166). In many cases, it was the genetics of the tumor and not the treatment the patient received that allowed for prolonged survival. Biotherapy The sulindac sulfone exisulind derivatives CP248 and 461 in cultured GBM cells arrested the cell cycle in the M phase, activated the pro-apoptotic protein kinase G, perturbed microtubule polymerization, and caused cell death [167]. The inhibitory pseudosubstrate sequence within the enzyme PKC (see Part II) is antagonistic to the enzyme and to the growth of GBM cells [168]. The geldanamycin derivative 17-AAG is being tested against many xenografted human tumors (see Part IV), including GBM cells, and it appears to be growth inhibitory in most of the assays. Glioblastoma multiforme cells overexpress the Th2 cytokine IL-13 receptor. An immunotoxin has been constructed—IL-13-PE38QQR—which consists of IL-13 and Pseudomonas exotoxin fusion protein. It kills xenografted human GBM cells [169–172]. Another immunotoxin targets IL-4R. Stereotactically assisted local injection of the IL-4 (3837)-PE38KDEL immunotoxin induced extensive necrosis and occasional CR of highly malignant brain tumors. Transferrin linked to diphtheria toxin attaches to its receptor on GBM cells and the complex is endocytosed, with cell death resulting [173–175]. Human leukocyte antigen-A0201–restricted immune T lymphocyte clones cytotoxic to GBM cells expressing IL-13R␣2 could be generated in vitro [176]. Epidermal growth factor-R expression is minimal, if any, in the normal brain, while there is cross-reactivity of IL-13 with IL-3R. Targeting EGF-R with fusion proteins (immunotoxins) therefore offers the highest safety profile [172]. Epidermal growth factor and diphtheria toxin fusion protein DAB389EGF preferentially kills tumor cells with dense expression of EGF-R, but it certainly could induce liver and kidney toxicity; however, its clinical efficacy was inhibited by pre-existing antidiphtheria toxin antibodies [177,178]. Neural stem cells (NSC) exhibit tropism toward GBM cells. Transfected with the IL-12 gene or with


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the ligand TNF␣ and injected intracranially into murine gliomas, the genetically engineered NSC cells killed the glioma cells [179,180]. Gap junction communications regulate intercellular relationships through expression of connexins (see Part IV). Connexin 43 (cx43) is underexpressed in GBM cells. Transfection of cx43 gene into GBM cells (also into leiomyo- and rhabdomyosarcoma cells) reversed the malignant phenotype and reduced MCP-1 overexpression by the tumor cells. Connexin 43 downregulates monocyte chemotactic protein in GBM cells, depriving the tumor of one of its prominent growth factors [181,182]. The anti-apoptotic chaperone protein Hsp70 is highly overexpressed in GBM cells. Adenoviral (Ad.asHsp70) introduction of antisense Hsp70 cDNA into GBM cell orthotopic xenografts (also into breast and colon carcinoma xenografts) eradicated the xenografts [183]; GBM cells were wiped out through phagocytosis by macrophages. Neuroblastoma cells are protected from chemotherapy-induced apoptosis by brain-derived neutrophilic factor (BDNF) activation mediated by tyrosine kinase receptors. Inhibitors K252 or LY294002 (aimed at PI3K) reversed the protective effect; MAPK inhibitor PD98059 or peritoneal lymphocyte ␥ inhibitor U73122 were inefficient [184]. A naturally occurring fragment of human MMP-2 is anti-angiogenic and inhibits cell proliferation and invasiveness. The hemopexin fragment PEX binds to integrin ␣␯␤3 and suppresses growth of GBM xenografts without toxicity; platelet factor-4 (PF-4) acts additively in this system [161,185,186]. The Hungarian team successfully uses adenoviral vectors to deliver genes for specific enzymes (v-tk), cytokines (Il-2, IL4, IL-12, TNF␣), or hematopoietic growth factors (GM-CSF) into murine and human glioblastoma cells for the sensitization of these cells to chemotherapeuticals (5 FU; ganciclovir) or to render them more immunogenic [187,188]. Herpes simplex virus-1 tk driven by cytomegalovirus (CMV) promoter and delivered by intact E1AB-containing adenoviral vector (IG.Ad5E1Ⳮ.E3TK) into GBM cells rendered the tumor cells highly susceptible to ganciclovir-induced apoptotic death [189]. Clinical results of tk gene transfer into malignant gliomas with

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replication-defective retroviral vectors were so far unsuccessful because of very low transduction efficiency. Transduction efficiency for p53 adenoviral gene transfer was also low [190]. Modified replication-competent retroviral vectors (MuLV unable to infect quiescent normal cells, but replicating selectively in dividing tumor cells) performed with greatly increased transduction efficiency without infecting normal brain cells and without systemic dissemination in the body (negative PCR for viral genomic segments) [191,192]. Clinical trials are planned in Los Angeles, CA. These retroviral vectors can also insert the yeast cytosine deaminase gene into tumor cells, sensitizing the cells to 5-fluorocytosine. Adenoviral vectors have been constructed for the restoration of PTEN, the anti-neoangiogenic gene product proteins–(Ad)-wt-PTEN and Ad-G129E-PTEN for the treatment of PTENⳮ prostate cancer (PC3) and GBM cells (see Part I). In these cells, COX-1 and COX-2 were not inhibited, but VEGF production was decreased. Glioblastoma multiforme cells were arrested in G1 and lost their metastatic potential, but did not die apoptotic death. Adenoviral vectors of p53 gene performed poorly, even after repeated attempts at transduction of glioma cells, because of underexpression of CAR resulting in low transduction efficiency [190]. Glioblastoma multiforme cells activate MMP-9 secretion after binding uPA to its receptor uPAR. The replication-defective serotype 5 adenovirus AduPAR-MMP-9 contains antisense oligonucleotides disabling transcription of both targeted genes [193]. Matrix metalloproteinase-9 degrades extracellular matrix and facilitates the invasiveness of the tumor cell. Expression of both uPAR and MMP-9 were suppressed in transfected GBM cells and the transfected tumor cell spheroids failed to invade normal neural tissues in co-cultures. As-ODN treatment directed at laminin-8 of glioma cells suppressed their locomotion [194]. Liposome-encapsulated genetically engineered Semliki forest arbovirus delivered the gene of IL-2 into GBM cells and augmented the immune responses these tumor cells evoked [195]. The phosphorothioate antisense oligodeoxynucleotide IGF-IR/ AS ODN (Lynx Therapeutics, Des Moines, IA) targets the IGFR gene. Surgically removed astrocytomas were treated with


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As-ODN and reimplanted into the patient’s rectus sheath, where the tumor underwent apoptotic death and induced lymphocytic infiltrations [196]; this method of gene therapy may work as a glioma vaccine (vide infra). The technology of gene therapy is improving by an enhanced delivery system [197]. No malignant entity mobilized more intensive efforts for viral therapy than GBM and other brain tumors. Adeno-, adeno-associated, herpes-, reo-, and retroviral vectors have been extensively tested. A genetically engineered adenovirus becomes the vector of a transgene, when a selected gene is cloned into a plasmid, which is recombined with another plasmid possessing adenoviral packaging signal; forming virions become vectors of the transgene. Adenovirus with E1B deleted (ONYX) is restricted to replicate only in tumor cells with defective p53 gene (see Part I). Adenoviral genomes occupy extrachromosomal positions in the cell and adenoviral capsids are antigenic in the host; CAR viral entry sites are underexpressed on many tumor cells that remain uninfected. In this way, adenovirally infected cells may get rid of the virus and extracellular virus is often neutralized by antibodies. Adenoviruses delivered the herpesviral tk gene, the wild-type p53 gene, and various cytokine genes (IL-2, IL-12, IFN-␥) and hematopoietic growth factor genes (GM-CSF) into brain (and other) tumor cells. Adenoviruses have 10-kb transgene capacity, but grow to high titers. Adeno-associated viruses seek out the 19q chromosomal locus for the integration of their genome in human cells. They cannot accommodate a transgene larger than 4.7 kb and grow in low titers. The multimutated HSV-1 G207 or the ␥34.5 mutant HSV1 1716 act as oncolytic agents without a transgene incorporated into their genomes. Reoviruses are expected to perform similarly. Retroviruses recognize long terminal repeats (LTR) as packaging signals and incorporate transgenes inserted between two LTR. The NCI murine fibroblast line 3T3 serves as vector producer cells transfected with the retroviral genome (Moloney mouse leukemia virus) and the transgene. Retroviral vectors grow in low titers, accept transgenes not larger than 7.5 kb, but enter the nuclei of dividing (not resting) cells and

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do not pose a high antigenic impact on the host. The vectorproducer cells have to be engrafted into the targeted tumors (requiring many needle punctures); the unstable retroviral particles seldom infect tumor cells otherwise. When tumor cells incorporating the herpes virus tk gene are exposed to acyclovir or ganciclovir, they die. The ‘‘bystander effect’’ consists of cell death other than that of transfected tumor cells and that of unintentionally tk-transfected vascular endothelial cells. There is host immunity to the herpes viral enzyme protein Tk and there is cell-to-cell transfer of ganciclovir triphosphate through gap junctions. In all tumor categories treated with herpes viral tk-transfection, including GBM cells, objective and clinically beneficial response rate barely exceeds 10%. In more than 30 brain tumor clinical trials with various oncolytic viruses and viral vectors, no major adverse effects (no viral encephalitis, not even with the herpes viral mutants) occurred. Decrease in tumor size, stagnation (stabilization), and delayed progression of disease is commonly observed; it is more often a trend, rather than a statistically significant delay in tumor progression that is recorded. Rare cases are on the record with tumor regression and no relapse within 2 years [198]. In 2001, at the 33rd Annual Scientific Meeting of the Hungarian Medical Association of America in Sarasota, FL, the United Cancer Research Institute (Alexandria, VA), and the Hadassah University (Jerusalem, Israel) announced remission inductions in patients with malignant gliomas treated with the attenuated veterinary NDV vaccine, which is used in Hungary to vaccinate poultry (without any further development, this virus was renamed MTH-68H for the purpose of human use). However, no published concise report followed in the ensuing 2 years. Major improvements in viral therapy of GBM (and other tumors) are required for better and confirmed clinical results. Epidermal growth factor-RvIII yields immunogenic peptides; when it was used with KLH adjuvant for active gliomaspecific preventive immunization of mice, it enabled the animals to reject live glioma cell inocula [199,200]. Glioma cellassociated antigens, perhaps those expressed by fusion oncoproteins such as the ROS-FIG oncoprotein [201], when re-


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ceived by mature DC either as downloaded peptides or as tumor genomic mRNA /cDNA to be processed internally in the DCs also co-expressing IL-12 or as fusion partners forming chimeras of autologous irradiated glioma cells with live DC, induced T cell immunity because DCs presented glioma cell antigens to T lymphocytes for IL-2–mediated expansion of the immune T cell clone [202,203]. Clones of CD8 specifically cytotoxic to autologous glioma cells arose in the immunized patients. Glioma cells transfected with the IFN-␤ gene carried by a retroviral vector plasmid (pSV2-IFN-␤/pDONAI, Takara Bio, Otsu, Shiga, Japan) stimulated DC best and induced T cell clones highly cytotoxic to murine glioma cells [204]. Tumor cells, among them GBM cells, are able to express FasL to kill Fas receptor-positive host lymphocytes, but GBM cells are not exempt from FasL-mediated programmed cell death. Taurolidine enhances FasL-mediated apoptosis of glioma cells [205,206]. Glioblastoma multiforme cells obliterate an immune response from the host. These cells do not express the costimulatory molecules B7.1/2; instead they display B7-H1, which is an inhibitor of CD4/CD8 lymphocytes in that it suppresses IL2 production and the expression of T cell activation marker CD96 [207]. Some malignant gliomas elicit a specific T cell response, which could be intensified by active tumor-specific immunotherapy with DC vaccines [176]. Autotumor-specific T lymphocytes were generated by co-culturing lymphocytes with autologus tumor cells. Topical administration of such lymphocyte populations to five patients with anaplastic astrocytomas resulted in one CR and four PR. In a summary of lymphocyte therapy for GBM and anaplastic astrocytomas (occasionally including melanoma metastatic to the brain), autologous lymphocyte preparations were infused through Ommaya reservoirs or burr holes into the cavities left behind after incomplete surgical removal of the primary tumor or at the time of relapse after postoperative radiotherapy. Interleukin-2 was given systemically to expand the infused lymphocyte population. The University of North Carolina at Chapel Hill used tumor-infiltrating lymphocytes (TIL) in six patients and recorded one CR, two PR and two stabilizations of the disease, with three deaths

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attributable to eventual progression of the disease. In five clinical trials with LAK cells and reported from Bethesda, MD; New York, NY; India; and Japan, 48 patients were treated; 8 CR, 10 PR, and many stabilizations of disease occurred. Treated groups experienced median survival over 53 to 55 weeks vs. median survival of 25 weeks in the conventionally treated control group. In one trial (Kaplan CCC, New York) 8 of 15 treated and 1 of 18 control patients were alive at the time of the report. Occasionally, brain edema (attributable to the restricted use of corticosteroids) or intratumoral hemorrhage occurred. A young man in Japan with anaplastic glioma survived 9 years after conventional therapy, but relapsed; LAK cell therapy induced another CR [208]. Alloreactive cytotoxic T cells sensitized with the patient’s MHC proteins were instilled into the cavitary lesions left behind after surgical removal of malignant gliomas; of five patients, two survived over 28 and 30 months without tumor recurrence [209–218]. Of monoclonal antibodies directed at glioma cells [219], antitenascin immunotoxin has been tested. Tenascin enabled melanoma cells to detach from their matrix and invade; this mediator is also active in GBM. The I131-labeled antitenascin monoclonal antibody (McAb 81C6) was infused into cavities left behind after incomplete surgical removal of highly malignant brain tumors. Duke University (Durham, NC) reports prolongation of life up to 69 to 79 weeks with minimal toxicity if the 120-mCi total dose was not exceeded [220,221]. Standard therapy of GBM is not curative, but is undergoing steady improvements: Irinotecan; nimustine, teniposide, and cytarabine are added to radiotherapy in Germany (NeuroOncology Working Group of the German Cancer Society); temozolomide is used at reduced dosage continuously and its efficacy is increased by the co-adminstration of the poly(ADP-ribose) polymerase-1 inhibitor GP 15427 or CEP-6800 [222,223]. Of neoangiogenesis inhibitors, thalidomide and IFN-␣ are in clinical trials. In its first trials, thalidomide (see Part IV) induced 2 PR, 2 MR, and 12 stabilizations of the disease [224]. SU112448 (Sugen) [225], ZD1839 (gefitinib, Iressa), OSI-774 (erlotinib, Tarceva), anti-ErbB (ABX-EGF) TKIs (see Part I), and anti-VEGF (bevacizumab, Avastin) monoclonal antibody


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(see Part III) are in advanced clinical trials showing additive, or better— sometimes synergistic—efficacy. Glioma cells overexpress COX-1 and COX-2, and COX or thromboxane synthetase inhibitors suppress their growth and render the tumor cells more susceptible to chemotherapy (camptothecins) [226]. Even nonconventional treatment modalities, such as the alkaloid mixture ruta-6, the extract of Ruta graveolens, may score clinical responses (reportedly CR!) [227]. The most accurate way to measure tumor responses in the brain is by 201T-SPECT (single-photon emission computed tomography) scanning [228]. REFERENCES, PART V 1. Kyle RA. Diagnosis of multiple myeloma Semin Oncol 2002; 29(6 Suppl 17):2–4. 2. Barlogie B, Shaughnessy J, Zangari M, Tricot G. High-dose therapy and immunomodulatory drugs in multiple myeloma Semin Oncol 2002; 29(6 Suppl 17):26–33. 3. Rajkumar SV, Kyle RA, Gertz MA. Myeloma and the newly diagnosed patient: a focus on treatment and management Semin Oncol 2002; 29(6 Suppl 17):5–10. 4. Kumar A, Loughran T, Alsina M, Durie BG, Djulbegovic B. Management of multiple myeloma: a systematic review and critical appraisal of published studies Lancet Oncol 2003; 4: 293–304. 5. Attal M, Harousseau JL, Facon T, Guilhot F, Doyen C, Fuzibet JG, Monconduit M, Hulin C, Caillot D, Bouabdallah R, Voillat L, Sotto JJ, Grosbois B, Bataille R. Single versus double autologous stem-cell transplantation for multiple myeloma N Engl J Med 2003; 349:2495–2502. 6. Alain T, Thirukkumaran C, Morris DG, Urbanski SJ, Janowska-Wieczorek A, Lee PWK, Kossakowska AE. Lymphomas and oncolytic virus therapy Clinical Lymphoma 2003; 4: 104–111. 7. Kuehl WM, Bergsagel PL. Multiple myeloma: evolving genetic events and host interactions Nat Rev Cancer 2002; 2:175–187.

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tors expressing human p53 gene by repeated transduction into glioma cells Clin Cancer Res 2002; 8:913–921. 191. Wang WJ, Tai CK, Kasahara N, Chen TC. Highly efficient and tumor-restricted gene transfer to malignant gliomas by replication-competent retroviral vectors Hum Gene Ther 2003; 14:117–127. 192. Solly SK, Trajcevski S, Friseń C, Holzer GW, Nelson E, Clerc B, Abordo-Adesida E, Castro M, Lowenstein P, Klatzmann D. Replicative retroviral vectors for cancer gene therapy Cancer Gene Ther 2003; 10:30–39. 193. Adachi Y, Chandrasekar N, Kin Y, Lakka SS, Mohanam S, Yanamandra N, Mohan PM, Fuller GN, Fang B, Fueyo J, Dinh DH, Olivero WC, Tamiya T, Ohmoto T, Kyritsis AP, Rao JS. Suppression of glioma invasion and growth by adenovirus-mediated delivery of a bicistronic construct containing antisense uPAR and sense p16 gene sequences Oncogene 2002; 21: 87–95. 194. Khazenzon NM, Ljubimov AV, Lakhter AJ, Fujita M, Fujiwara H, Sekiguchi K, Sorokin LM, Petajaniemi N, Virtanen I, Black KL, Ljubinova JY. Antisense inhibition of laminin-8 expression reduces invasion of human gliomas in vitro Mol Cancer Ther 2003; 2:985–994. 195. Ren H, Boulikas T, Soling A, Warnke PC, Rainov NG. Immunogene therapy of recurrent glioblastoma multiforme witha liposomally encapsulated replication-competent Semliki forest virus vector carrying the human interleukin-12 gene: phase I/II clinical protocol J Neurooncol 2003; 64:147–154. 196. Andrews DW, Resnicoff M, Flanders AE, Kenyon L, Curtis M, Merli G, Basergo R, Iliakis G, Aiken RD. Results of a pilot study involving the use of an antisense oligodeoxynucleotide directed against the insulin-like growth factor type I receptor in malignant astrocytomas J Clin Oncol 2001; 19:2189–2200. 197. Voges J, Reszka R, Gossman A, Dittmar C, Richter R, Garlip G, Kracht L, Coenen HH, Sturm V, Wienhard K, Heiss WD, Jacobs AH. Imaging-guided convection-enhanced delivery and gene therapy of glioblastoma Ann Neurol 2003; 54:479–487. 198. Chiocca EA, Aghi M, Fulci G. Viral therapy for glioblastoma Cancer J 2003; 9:167–178.

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199. Kuan C-T, Wikstrand CJ, Bigner DD. EGF mutant receptor vVIII as a molecular target in cancer therapy. Abstract. Duke University Medical Center, Durham NC 27710. 200. Heimberger AB, Crotty LE, Archer GE, Hess KR, Wikstrand CJ, Friedman AH, Friedman HS, Bigner DD, Sampson JH. Epidermal growth factor receptor VIII peptide vaccination is efficacious against established intracerebral tumors Clin Cancer Res 2003; 9:4247–4254. 201. Charest A, Lane K, McMahon K, Park J, Preisinger E, Conroy H, Housman D. Fusion of FIG to the receptor tyrosine kinase ROS in a glioblastoma with an interstitial del [6] (q21q21) Genes Chromosomes Cancer 2003; 37:58–71. 202. Yamanaka R, Yajima N, Abe T, Tsuchiya N, Homma J, Narita M, Takahashi M, Tanaka R. Dendritic cell-based glioma immunotherapy (Review) Int J Oncol 2003; 23:5–15. 203. Insug O, Ku G, Ertl HC, Blaszczyk-Thurin M. A dendritic cell vaccine induces protective immunity to intracranial growth of glioma Anticancer Res 2002; 22:613–621. 204. Nakahara N, Pollack IF, Storkus WJ, Wakabayashi T, Yoshida J, Okada H. Effective induction of antiglioma cytotoxic T cells by coadministration of interferon-␤ gene vector and dendritic cells Cancer Gene Ther 2003; 10:549–558. 205. Glaser T, Wagenknecht B, Groscurth P, Kramer PH, Weller M. Death ligand/receptor-independent caspase activation mediates drug-induced cytotoxic cell death in human malignant glioma cell Oncogene 1999; 18:5044–5053. 206. Stendel R, Scheurer L, Stoltenburg-Didinger G, Brock M, Mohler H. Enhancement of Fas-ligand-mediated programmed cell death by taurolidine Anticancer Res 2003; 23:2309–2314. 207. Wintterle S, Schreiner B, Mitsdoerffer M, Schneider D, Chen L, Meyermann R, Weller M, Wiendt H. Expression of the B7related molecule B7H1 by glioma cells: a potential mechanism of immune paralysis Cancer Res 2003; 63:7462–7467. 208. Naganuma H, Sasaki A, Satoh E, Nagasaka M, Isoe S, Nakano S, Nukui H. Long-term survival in a young patient with anaplastic glioma Brain Tumor Pathol 1997; 14:71–74. 209. Quattrocchi KB, Miller CH, Cush S, Bernard SA, Dull ST, Smith M, Gudeman S, Varia MA. Pilot study of local autolo-


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gous tumor infiltrating lymphocytes for the treatment of recurrent malignant gliomas J Neurooncol 1999; 45:141–157. 210. Sankhla SK, Nadkarni JS, Bhagwati SN. Adoptive immunotherapy using lymphokine-activated killer (LAK) cells and interleukin-2 for recurrent malignant primary brain tumors J Neurooncol 1996; 27:133–140. 211. Hayes RL, Koslow M, Hiesiger EM, Hymes KB, Hochster HS, Moore EJ, Pierz DM, Chen DK, Budzilovich GN, Ransohoff J. Improved long term survival after intracavitary interleukin-2 and lymphokine-activated killer cells for adults with recurrent malignant glioma Cancer 1995; 76:840–852. 212. Nakagawa K, Kamezaki T, Shibata Y, Tsunoda T, Meguro K, Nose T. Effect of lymphokine-activated killer cells with or without radiation therapy against malignant brain tumors Neurol Med Chir (Tokyo) 1995; 35:22–27. 213. Thomas C, Schober R, Lenard HG, Lumenta CB, Jacques DB, Wechsler W. Immunotherapy with stimulated autologous lymphocytes in a case of a juvenile anaplastic glioma Neuropediatrics 1992; 23:123–125. 214. Hayes RL. The cellular immunotherapy of primary brain tumors Rev Neurol (Paris) 1992; 148:454–466. 215. Barba D, Saris SC, Holder C, Rosenberg SA, Oldfield EH. Intratumoral LAK cell and interleukin-2 therapy of human gliomas J Neurosurg 1989; 70:175–182. 216. Kruse CA, Cepeda L, Owens B, Johnson SD, Stears J, Lillehei KO. Treatment of recorrent glioma with intracavitary alloreactive cytotoxic T lymphocytes and interleukin-2 Cancer Immunol Immunother 1997; 45:77–87. 217. Tsuboi K, Saijo K, Ishikawa E, Tsurushima H, Takanoi S, Morishita Y, Ohno T. Effects of local injection of ex vivo expanded autologous tumor-specific T lymphocytes in cases with recurrent malignant gliomas Clin Cancer Res 2003; 9: 3294–3302. 218. Nagane M, Oyama H, Shibui S, Nomura K. Recurrence with tumor bleeding in a patient with malignant astrocytoma during the treatment with intracranial injection of lymphokineactivated killer cells—a case report No To Shinkei 1993; 45: 547–551.

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219. Papanastassiou V, Pizer BL, Chandler CL, Zananiri TF, Kemshead JT, Hopkins KI. Pharmacokinetics and dose estimates following intrathecal administration of 131I-monoclonal antibodies for the treatment of central nervous system malignancies Int J Radiat Oncol Biol Phys 1995; 31:541–552. 220. Bigner DD, Brown MT, Friedman AH, Coleman RE, Akabani G, Friedman HS, Thorstad WL, McLendon RE, Bigner SH, Zhao XG, Pegram CN, Wikstrand CJ, Herndon JE, Vick NA, Paleologos N, Cokgor I, Provenzale JM, Zalutsky MR. Iodine131-labeled antitenascin monoclonal antibody 81C6 treatment of patients with recurrent malignant gliomas: phase I trial results J Clin Oncol 1998; 16:2202–2212. 221. Cokgor I, Akabani G, Kuan CT, Friedman HS, Friedman AH, Coleman RE, McLendon RE, Bigner SH, Zhao XG, GarciaTurner AM, Pegram CN, Wikstrand CJ, Shafman TD, Herndon JE, Provenzale JM, Zalutsky MR, Bigner DD. Phase I trial results of iodine-131-labeled antitenascin monoclonal antibody 81C6 treatment of patients with newly diagnosed malignant gliomas J Clin Oncol 2000; 18:3862–3872. 222. Virag L, Szabo C. The therapeutic potential of poly(ADP-ribose) polymerase inhibitors Pharmacol Rev 2002; 54:375–429. 223. Tentori L, Leonetti C, Scarsella M, d’Amati G, Vergati M, Portarena I, Xu W, Kalish V, Zupi G, Zhang J, Graziani G. Systemic administration of GPI 15427, a novel poly(ADP-ribose) polymerase-1 inhibitor, increases the antitumor activity of temozolomide against intracranial melamoma, glioma, lymphoma Clin Cancer Res 2003; 9:5370–5379. 224. Fine HA, Wen PY, Maher EA, Viscosi E, Batchelor T, Lakhani N, Figg WD, Purow BW, Borkowf CB. Phase II trial of thalidomide and carmustine for patients with recurrent high-grade gliomas J Clin Oncol 2003; 21:2299–2304. 225. Schueneman AJ, Himmelfarb E, Geng L, Tan J, Donnelly E, Mendel D, McMahon G, Hallahan DE. SU11248 maintenance therapy prevents tumor regrowth after fractionated irradiation of murine tumor model Cancer Res 2003; 63:4009–4016. 226. Kurzel F, Hagel C, Zapf S, Meissner H, Westphal M, Giese A. Cyclo-oxygenase inhibitors and thromboxane inhibitors differentially regulate migration arrest, growth inhibition and


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apoptosis in human glioma cells Acta Neurochir 2002; 144: 71–87. 227. Pathak S, Multani AS, Banerji P, Banerji P. Ruta 6 selectively induces cell death in brain cancer cells but proliferation in normal peripheral blood lymphocytes: a novel treatment for human brain cancer Int J Oncol 2003; 9:975–982. 228. Perry JR, Cairncross JG, Busam KJ. Glioma therapies: how to tell which work? J Clin Oncol 2003; 21:3547–3551.

DISCUSSION This chapter omitted review of the extensive use of preventive and therapeutic tumor vaccines (however, viral oncolysate cancer vaccines are described) and lymphocyte therapy, extending from melanoma and kidney carcinoma (the National Cancer Institute protocols) to other tumor categories, receives only some brief remarks. Only a few examples of the rapidly enlarging field of monoclonal antibodies and immunotoxins are mentioned because many of these agents are not in Phase I or Phase II trials any longer, but receive now full credit and have become respected and licensed therapeutic modalities. These include rituximab (Rituxan, Genentech) for CD20Ⳮ lymphomas and trastuzumab (Herceptin, Genentech) for HER2/ neuⳭ breast carcinomas. Iodine131-labeled tostitumomab (Bexxar, Aventis Pasteur) is a licensed monoclonal antibody inducing remissions in patients with chemo-radiotherapy– resistant malignant lymphomas. The latest addition is ibritumomab tiuxetan, the Y90-labeled monoclonal antibody (Zevalin, Idec) directed at the CD20 antigen of B-lineage lymphoma cells. Not only cognate ligands of targeted receptors (Tac for IL-2, IL-4, IL-13) linked with cytotoxins, but antibodies directed at cell surface receptors, could also be linked to such a toxin (Pseudomonas or diphtheria exotoxin). These are the LMB immunotoxins, one of which, the anti-CD22 BL22, is awaiting approval for the treatment of hairy cell leukemia. Another, the calicheamicin-containing gemtuzumab ozogamicin (Mylotarg, Wyeth/Genetics), aimed at CD33 of AML cells, has completed all its pre-licensure clinical trials. Denileukin

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diftitox (Ontak, Ligand Pharmaceuticals, San Diego, CA) attacks IL-2R-overexpressing T lymphoma cells. The anti-CD22 epratuzumab and the anti-CD52 alemtuzumab (Campath-1H, Berlex Laboratories, Seattle, WA (PDR p. 932 2004)) induce remissions in cases of lymphomas and B-CLL refractory to chemotherapy. The anti–CA-125 oregovomab delays postoperative relapses in patients with ovarian carcinoma. This tumor is targeted for mumps, measles, NDV, and reoviral therapy. Is there a rationale to combine viral therapy with the antibody? Of IMIDs, CC-5013 (Revimid, Celgene) is already in advanced clinical trials for MM and GBM. Of inhibitors of VEGF and its receptor, the indolinones SU5416 (semaxanib) and SU6668; the anilinoquinazoline ZD6474; the anti-Flt-1 ribozyme; and the cyclodepsipeptide aplidine (from Aplidium albicans) reached the Phase I and Phase II clinical trial stage. Although the idea to combine TKIs and monoclonal antibodies shines as a most brilliant one (Iressa and Herceptin for breast cancer; Tarceva and Avastin for NSCLC, except squamous cell carcinomas, or for GBM), the preliminary clinical results are somewhat below expectations given that CR remain rare achievements. The question arises whether naturally oncolytic or genetically engineered viruses would fit into any of these combinations. Omitted for review are the retinoic acid derivatives that induce differentiation of malignant cells. Some of these are licensed therapeutic agents, others are widely used to suppress precancerous lesions, such as oral leukoplakia, and to prevent head and neck squamous cell and many other carcinomas. These trials are dealt with in detail in textbooks of medical oncology. Patients with acute promyelocytic/progranulocytic leukemia (APL) suffer the characteristic translocation t(15;17)(q22;q12), where the breakpoint on chromosome 17 is at the intron of the retinoic acid receptor gene ␣ (RAR␣). Alltransretinoic acid (ATRA) induces differentiation of these leukemia cells (but for durable CR, combination chemotherapy is required). Retinoids selective for Tac-101 RAR␣ occasionally induce a remission in patients with metastatic cancers. Otherwise, 13-cis RA, fenretidine, vitamin D analogue ILX23-7533, and tazarotene failed to elicit any tumor response. However,


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bexarotene (Targretin) emerges as the retinoid-receptor agonist that induces apoptotic death of squamous carcinoma cells and prolongs the survival of patients with NSCLC who receive it in combination with chemotherapy. Perhaps another protocol (recall the one initiated by M. D. Anderson Cancer Center in Mexico for squamous cell carcinoma of the uterine cervix) combining RA derivatives with IFN-␣ would score; this combination is being now tested Eastern Cooperative Oncology Group (ECOG) in patients with squamous cell carcinoma of the penis. Could some of the oncolytic viruses be combined with RA derivatives in a clinical trial? If these tumors are caused by certain subtypes of HPV, viral interference and antitumor vaccination applied together may explain the susceptibilty to virally induced regression of these tumors. This chapter was written at the time when the 2003 American Association for Cancer Research Congress in Toronto was canceled and the ASCO Conference in Chicago was to be held 1 month later. Although the Proceedings of both of these conferences (AACR vol. 44, 2003; ASCO vol. 22, 2003) are replete with abstracts of TKIs and anti-neoangiogenesis agents and other new biotherapeuticals, oncolytic viruses remain underrepresented in them; only adenoviral constructs for gene therapy receive some attention. A new biochemotherapy protocol for per os and out-patient administration emerges for the treatment of metastatic malignant melanoma (ASCO 噛2881, 2003): temozolomide (Temodar, Schering), GMCSF (sargramostim, Leukine, Immunex), IFN-␣2b (Intron, Schering, Seattle, WA), and IL-2 (aldesleukine, Proleukine, Chiron, Emeryville, CA). This regimen induced 16% CR and 16% PR rates and stabilization of disease in 28% of patients with ‘‘acceptable’’ toxicities consisting of ‘‘flu-like’’ symptoms. Could any oncolytic virus match this efficacy of a treatment modality? If not, either only those patients who fail (progressive disease in 40% of patients) would be acceptable for viral therapy, or viral therapy (in the form of a viral oncolysate or a DC vaccine) should be incorporated in the chemobiotherapy protocol. Bulletins from the Institute of Drug Development issued by the Cancer Therapy and Research Center in San Antonio, TX, publish serial reports on new cancer therapeuti-

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cals entering clinical trials. In the last issues of Oncology Times (volume XXV/18–19, September 25, October 10, and October 25, 2003) there is a much-abbreviated listing of newly approved clinical trials. It is an overwhelming list in which viral therapy of human cancers is conspicuously underrepresented. In 1986, Marcel Dekker published the single-authored textbook ‘‘Medical Oncology, an Advanced Course’’, second edition, in two volumes comprising 2062 pages and based on some 25,000 references. In the Preface, the author expressed his hope that the immediate and long-term toxicities of chemotherapy will somehow be ameliorated and that biological means of treating cancer will gain ground and that we shall be able to communicate with our cells, even malignantly transformed cells, using the cells’ own vocabulary and language. In the past few years, the biological treatment of cancer has become a reality at many levels. Tyrosine kinase inhibitors are suppressing signal transduction from oncogenes: The malignant cell follows our orders to the extent that it surrenders to its apoptotic death. We learned which cytokines or chemokines favor the host and oppose the tumor. The antigenicity of some point-mutated (Ras; Her2/neu), truncated (EGF-RvIII), or fusion (Bcr/Abl) oncoproteins opens up avenues for the use of preventive and therapeutic tumor-specific vaccinations. Autologous immune T cell clones rise against amplified or mutated survivins or telomerases (Inter J Oncol 2004; 25:211–7; POR Sept. 2004) and gefitinib works best against mutated EGF–R (Nature Med. 2004; 10:577–8). Monoclonal antibodies deriving from immune plasma cells fused with immortalized lymphoid cells (B. H. Tom and J. P. Allison, The University of Texas Medical School, Houston, TX, eds; ‘‘Hybridomas and Cellular Immortality’’, Plenum Press, New York and London, 1981; pp 1–302) evolved into tumor-specific immunotoxins and agents of antitumor ADCC reactions. Rituximab-coated lymphoma cells are phagocytized by dendritic cells (DC). These DC then induce immune T cell clones that kill the lymphoma cells in the patient (Th53. 319 Immunology 2004, Montreal, Canada). Lymphocytes (NK cells and immune T cells) found to be cytotoxic to tumor cells in the 1970s (In: J. G. Cory and A. Szenti-


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vanyi, The University of South Florida College of Medicine, Tampa, FL, eds.; ‘‘Cancer Biology and Therapeutics’’, Plenum Press, New York and London, 1986; pp 225–253) have become autologous LAK cells and TIL launching successful attacks on metastases. Adoptive immunotherapy with allogeneic NK lymphoid cells eradicates remnants of malignant cell populations at the price of tolerable graft-vs.-host disease. Means are now available to stop the subversion of the stroma by the tumor and to deprive the tumor of its nutrients and paracrine growth factors. Viral vectors deliver healthy genes into our disabled or mutated cells (with modest success rate). Genetically engineered or naturally oncolytic viruses pick and replicate in mutated and malignantly transformed cells and spare healthy cells of the tumor-bearing host. In the past 25 years, since the publication of the first monograph on cancer immunology-immunotherapy (J. E. Harris and J. G. Sinkovics, authors; The University of Texas M. D. Anderson Hospital, Houston, TX, ‘‘The Immunology of Malignant Disease’’ second edition, C. V. Mosby, St Louis, 1976; pp 1-606), our understanding of the cause and treatment of cancer has undergone fundamental changes. Biological therapy of cancer closes ranks with surgery, radio-, and chemotherapy. It will make the decisive contribution to the cure of cancer. SELECTED REFERENCES AACR-NCI-EORTC International Conference Molecular Targets and Cancer Therapeutics. Program & Proceedings Clin Cancer Research 2003; 9/16:6069s–6306s. Bast RC, Kufe DW, Pollock RE, Weichselbaum RR, Holland JF, Frei E. Cancer Medicine. 5th edition. Hamilton. Ontario. Canada: B.C. Decker, 2000:2546. Bronchud MH, Foote MA, Olopade O, Workman P. Principles of Molecular Oncology. Totowa. N.J.: Human Press, 2003:736. Figg WD, McLeod HL. Handbook of Anticancer Pharmacokinetics and Pharmacodynamics. Totowa. N.J.: Humana Press, 2004:650. Giordano A, Soprano KJ. Cell Cycle Inhibitors in Cancer Therapy. Totowa. N.J.: Humana Press, 2003:326.

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Greene JN. Infections in Cancer Patients. New York. N. Y.: Marcel Dekker, 2004:500. Harris RE. COX-2 Blockade in Cancer Prevention and Therapy. Totowa. N.J.: Humana Press, 2003:384. Levine MM, Kaper JB, Rappuoli R, Liu M, Good MF. New Generation Vaccines. New York. N.Y.: Marcel Dekker, 2004:1000. Lo BKC. Antibody Engineering. Totowa. N.J.: Humana Press, 2003: 576. Machida CSA. Viral Vectors for Gene Therapy. Totowa. N.J.: Humana Press, 2002:460. Murata H. Tumor-Suppressing Viruses, Genes and Drugs. San Diego. CA & New York N.Y.: Academic Press, 2003:325. Page´ M. Tumor Targeting in Cancer Therapy. Totowa. N.J.: Humana Press, 2002:466. Phillips MI. Antisense Therapeutics. Totowa. N.J.: Humana Press, 2004:300. Rak JW. Oncogene-Directed Therapies. Totowa. N.J.: Humana Press, 2003:487. Pitot HC. Fundamentals of Oncology. New York. N.Y.: Marcel Dekker, 2002:984. Sinkovics JG. Medical Oncology an Advanced Course. 2nd edition. Vol. I & II. New York. N.Y.: Marcel Dekker, 1986:2062. Syrigos KN, Harrington KJ. Targeted Therapy of Cancer. London. UK: Oxford University Press, 2003:343. Templeton N Smyth, Ed. (Baylor College of Medicine, Houston, TX). Gene and Cell Therapy. Marcel Dekker, New York, Basel, 2003-4.

SUMMARY Medical oncologists are close to being overwhelmed by the complexity of the selection process and by the abundance of the options when they are confronted by the patient who failed conventional therapy and is to be enrolled in Phase I or II protocols; or who, under the influence of the Internet or other sources of sensation-seeking publicity, refuses conventional


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therapy in favor of a biotherapeutical agent that is in preclinical or Phase I or II trials. Viral therapy remains one of the choices; when applied as monotherapy, it should match or surpass the results of numerous other agents without increased risks, or else it will have to be integrated into the framework of the new premises of biotherapeuticals and with good rationale. There is no doubt now that single-treatment modalities will seldom kill out an entire cancer cell population because the individual cancer cell switches from one growth cascade to another and so reproduces itself. However, simultaneous or dose-dense sequential neutralization of more than two or three of the tumor cell’s proliferative pathways, coupled with efforts to modify the tumor’s subverted microenvironment so that it ceases supporting the growth of the tumor, are expected to obliterate the entire multiplicity of tumor cell clones.

3 Measles Virus: Improving Natural Oncolytic Properties by Genetic Engineering CHRISTOPH SPRINGFELD, ADELE FIELDING, KAH-WHYE PENG, EVA GALANIS, STEPHEN J. RUSSELL, and ROBERTO CATTANEO Molecular Medicine Program, Mayo Clinic Rochester Rochester, MN

A PATHOGEN WITH ONCOLYTIC PROPERTIES Measles is a highly contagious disease with a characteristic erythematous, nonpruritic, maculopapular rash that is preceded by an unspecific prodromal illness of malaise, cough, coryza, and fever [1,2]. Although an effective live vaccine has been available for more than 30 years, measles is still a significant cause of morbidity and mortality in countries with poor 459

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or no vaccination coverage. Thirty to forty million cases of measles, resulting in 777,000 deaths, have been estimated for the year 2000 [3]. Mortality is associated with extreme ages, underlying illness, low socioeconomic status, lack of access to medical care, and malnutrition. Fatalities can be caused by secondary infections such as bacterial pneumonia, which are facilitated by an immunosuppression typical for measles. About one in 1000 children develops postinfectious encephalitis that is fatal in about 10% of the patients and frequently leads to sequelae in the surviving patients. An extremely rare (1 in 105 infections) fatal complication of measles, subacute sclerosing panencephalitis, can occur several years after wildtype measles virus (MV) infection and is caused by a persisting brain infection with defective virus mutants [4]. Measles vaccination is one of the most cost effective and successful public health interventions. Measles virus was first isolated by J. F. Enders and T. C. Peebles in 1954 [5]. Subsequently, different attenuated life vaccines were developed by passaging the virus on chick cells [6]. Vaccination with the currently used vaccine strains is safe and effective in preventing infection with wild-type MV. Adverse effects more serious than a low-grade fever are very rare and consist mainly of anaphylactic reactions, probably against the gelatin that is present in the vaccine as a stabilizer [7]. Vaccination against MV is even recommended for HIV-infected children unless they are severely immunocompromised [8]. Circumstantial evidence suggests that infection with wildtype MV can lead to tumor regression. Similarly, occasional regressions of human cancer after natural infections with other viruses have been reported [9]. Several cases of regression of hematological malignancies after natural MV infection have been noted at different places around the world. S. A. Hernandez [10] describes a 10-year-old child from Cuba with histologically proven Hodgkin’s disease who contracted measles before radiotherapy could be started. The child had a complete remission; however, the Hodgkin’s lymphoma relapsed after 4 months. A. Z. Bluming and J. L. Ziegler describe a case of an 8-year-old boy in Uganda with Burkitt’s lymphoma that completely resolved without any antineoplastic therapy after accidental MV infec-

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tion [11]. Z. Zygiert reports the natural measles infection of 3 out of 98 children with Hodgkin’s lymphoma in a hospital in Poland; all three children showed a striking remission of the lymphomas [12]. Two children had ‘‘one slight relapse’’ that could be successfully treated by conventional therapy; the third child remained in remission for at least 6 years after diagnosis. H. C. Mota adds a case from Portugal, where a 23-month-old boy with Hodgkin’s lymphoma showed a complete remission after natural MV infection; this child also relapsed after 6 months and needed further treatment [13]. Remissions associated with natural MV infection have also been observed in patients with lymphoblastic leukemia. G. Pasquianucci describes two children in Italy who had longterm remissions after measles; however, these children were also treated with chemotherapy, and one of them also contracted rubella [14]. A girl in Cleveland who was no longer responsive to chemotherapy developed measles and had a complete remission. However, she also relapsed 3 weeks later and died shortly after that [15]. Although some of the authors of the case reports discussed the possibility of an experimental infection of cancer patients with MV as a means of cancer therapeutics, to our knowledge this approach has not been implemented. On the other hand, the occasional case reports have triggered in vitro studies and experiments in mouse cancer models that are described in this review. The encouraging results of these studies led to the submission of clinical trial protocols that are open or will open in the near future. Furthermore, the MV reverse genetics system that is available since 1995 allows genetic modification of the MV-vaccine strain to improve its oncolytic properties. MOLECULAR BIOLOGY AND REVERSE GENETICS Measles virus is an enveloped RNA virus that is a member of the genus Morbillivirus within the family Paramyxoviridae and the order Mononegavirales [2]. The negative-stranded,

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nonsegmented viral genome comprises 15,894 bases and encodes six structural and two nonstructural proteins. It is organized into six contiguous, nonoverlapping transcription units separated by three untranscribed nucleotides and codes for the six structural viral proteins in the following order (antigenome): 5′–N–P–M–F–H–L–3′ (Fig. 1A, center). The P cistron additionally encodes two nonstructural proteins: The C protein is translated from an overlapping open reading frame by ribosomal choice [16], whereas the V protein is translated from an RNA that is cotranscriptionally edited by insertion of one nucleotide [17]. The viral genome is tightly encapsidated by the nucleoprotein (N) and further associated with the viral RNA polymerase (L) and the phosphoprotein (P), which serves as a cofactor for the viral polymerase (Fig. 1B). The viral RNA and the three proteins N, P, and L form the ribonucleoprotein complex. The MV envelope contains two glycoproteins, the receptor-binding hemagglutinin (H) and the fusion protein (F). The matrix protein (M) is the assembly organizer, associated with the inner layer of the envelope, and interacts with the cytoplasmatic tails of the glycoproteins [18]. Recently, it has been demonstrated genetically that MV virions are polyploid [19], confirming earlier conclusions drawn for other Paramyxoviruses and based on microscopical and physical examination of virus particles [20]. Another important characteristic is that the levels of transcription of the genes reflect their position in the genome [21]. This fact is being exploited to produce foreign proteins at different levels by inserting their genes in different locations of the MV genome (see below). 䉴 Figure 1 (A) Schematic representation of the measles virus (MV) antigenome (center). Selected unique restriction sites are shown. The replacement of the H protein by hybrid proteins displaying specificity domains is depicted at the top, and the insertion of foreign genes in additional transcription units (ATU) at three different locations is illustrated at the bottom. The intergenic nontranscribed trinucleotide (tri) is symbolized by a black bar. (B) Diagram of a polyploid MV particle containing three genomes. The symbols for the nucleocapsid protein (N), phosphoprotein (P), matrix protein (M), fusion protein (F), hemagglutinin (H), and the RNA polymerase (L) are indicated.

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Measles virus enters the cell by binding to different receptors and subsequently fusing its envelope with the cellular membrane, a process executed by the F protein. Two cellular receptors have been identified, the ubiquitous CD46 [22,23] and the immune cell-specific signaling lymphocyte activating molecule (SLAM) [24]. Measles virus wild-type and vaccine strains differ in their receptor usage: Wild-type strains enter the cells preferentially by SLAM, whereas vaccine strains use CD46 more efficiently [25]. However, other MV receptors may exist [26]. Recovery of infectious MV from cloned cDNA was first achieved by the Billeter laboratory in 1995 [27]. The recovery system is based on a stable cell line that expresses the MV proteins N and P as well as T7-polymerase. When this cell line is transfected with a plasmid encoding MV RNA polymerase (L) and a plasmid encoding the full-length MV-antigenome, both driven by a T7-promoter, infectious virus can be recovered. An alternative system that involves modified vaccinia Ankara virus expressing T7 polymerase and three plasmids encoding the N, P, and L proteins under the control of a T7-promoter has also been reported [28]. The first infectious cDNA clone was mainly based on an attenuated laboratory strain of the Edmonston lineage. In the meantime, viruses have also been recovered from cDNA clones encoding wildtype MV [29] and the Moraten/Schwartz vaccine strain (V. von Messling and R. Cattaneo, unpublished data). The MV reverse genetics systems have been extensively used to characterize mutant viruses with deleted genes [30–33], genes exchanged between different strains [25,34–36], single amino-acid substitutions [37,38], and additional genes (Fig. 1A, bottom). Proteins expressed by recombinant MV include the reporters green fluorescent protein [39], chloramphenicol acetyl transferase [40], beta-galactosidase [41,42], and luciferase (K.-W. Peng, unpublished); the marker peptides soluble human carcinoembryonic antigen (shCEA) and human chorionic gonadotropin (␤hCG) [43]; proteins of other viruses—e.g., the hepatitis B surface antigen [44] and human immunodeficiency virus proteins [45]; and immuno-

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Table 1 Proteins Expressed from Additional Transcription Units Inserted at Different Positions in the Measles Virus Genome. Genomic position Reporters/trackers CAT GFP

-gal CEA hCG luciferase Effectors human IL12 mouse IL12

Upstream of N

After P

After H

X

X X

X

X X X X X X

human GM-CSF mouse GM-CSF HSV-TK

X X

E. coli CD

X

NIS

X

X X

X

X

References

Mrkic et al., 1998 Duprex et al., 1999; Hangartner and Billeter, personal communication Neumeister et al., 2001 Peng et al., 2002 Peng et al., 2002 Peng, unpublished Singh and Billeter, 1999 Devaux and Cattaneo, unpublished Fielding, unpublished Grote et al., 2003 Springfeld and Cattaneo, unpublished Springfeld and Cattaneo, unpublished Dingli et al., 2004

CAT chloramphenicol acetyl transferase; GFP green fluorescent protein; -gal beta-galactosidase; CEA carcinoembryonic antigen; hCG human chorionic gonadotropin; IL interleukin; GM-CSF granulocyte-macrophage colony-stimulatory factor; HSV-TK herpes simplex virus thymidine kinase; CD cytosine deaminase; NIS natrium-iodine symporter.

modulatory proteins—e.g., interleukin-12 [46] and granulocyte-macrophage colony-stimulatory factor (GM-CSF) [47] (Table 1). Until now, up to about 5 kb of foreign genetic material has been added to the MV genome without a profound negative effect on viral replication (L. Hangartner and M. A. Billeter, personal communication). Because of the pleomorphism of MV virions, there are no theoretical size limitations for the viral genome. The maximal amount of additional sequences that is tolerated by MV has not yet been determined.

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VIROTHERAPY OF HEMATOLOGICAL MALIGNANCIES Recently, the possible effect of MV on lymphoma cells suggested by the case reports mentioned above has been further investigated in vitro and in animal models [42]. After confirming that MV can infect and lyse the human lymphoma cell lines Raji and DoHH2 in vitro, MV was injected in tumors of these cell lines established in severe combined immunodeficiency (SCID) mice. In this study, the attenuated MV strain of the Edmonston (MV-Edm) lineage used caused regression of the established tumor xenografts in vivo. It was further shown that passively transferred antibodies against MV did not eliminate the antitumor effect of the intratumorally injected virus. Measles virus proteins and mRNA were detected in the tumors, and infectious virus was recovered from explanted tumors. In the light of these encouraging results, a Phase I clinical study of intratumoral injections in patients with non-Hodgkin’s lymphoma (NHL) has been approved. Patients will be injected with one or two doses of the commercially available Moratenvaccine strain. The inclusion criteria for this study being relatively strict, patient recruitment has initially been difficult. A significant antineoplastic activity was also observed recently when human myeloma xenografts were treated with MV [48]. The MV-Edm strain efficiently replicated in a variety of myeloma cell lines and in primary human myeloma cells from six different patients. The in vitro infection of the tumor cells resulted in a strong cythopathic effect with extensive syncytia formation that finally led to apoptotic death. When tumors were established in SCID mice using the myeloma cell line ARH-77 and injected with MV-Edm, they were completely eradicated. Even i.v. inoculation of MV-Edm led to a significant growth inhibition of RPMI 8226 tumors and to a complete regression of ARH-77 tumors in athymic mice. TREATMENT OF OVARIAN CANCER Another type of human cancer considered for treatment with MV is ovarian cancer. This disease is commonly diagnosed at

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an advanced stage [49]. The patients are initially treated with surgery and chemotherapy, but most patients ultimately die from recurrent disease. Recurrent ovarian cancer is a promising target for intraperitoneal virotherapy because, in many patients, the disease does not spread beyond the peritoneal cavity. Viruses injected intraperitoneally will not be eliminated by circulating antibodies in the serum; however, antibodies in ascites may still interfere with infection. The effect of MV on ovarian cancer in vitro and in mouse models has been studied in detail using a trackable MV genetically engineered to produce carcinoembryonic antigen (CEA; MV-CEA) that is described in the following section [50]. In this study, MV was shown to be selectively oncolytic for ovarian cancer cells with minimal effects on normal cells. Treatment with MV enhanced the survival of athymic mice with s.c. and i.p. tumors of the ovarian cancer cell line SKOV3ip.1. Tumor infection in vivo was followed by monitoring the serum CEA levels of the mice. Based on the promising results achieved, a Phase I doseescalation trial of intraperitoneal administration of MV-CEA in advanced stage or recurrent ovarian cancer patients was planned. Only a minority of ovarian cancer patients (⬍10%–15%) express CEA, and these will be excluded as per the trial design. Detection of CEA in the serum therefore could serve as a good correlate of viral gene expression. This is the first clinical trial of therapeutic administration of a recombinant MV in humans. Extensive biodistribution [51] and toxicology testing has now been performed, and recombinant virus is being produced under good manufacturing practice conditions. An investigational new drug application has been approved by the Food and Drug Administration (FDA), and the clinical trial has begun in July 2004. TRACKABLE MEASLES VIRUS A common problem in the evaluation and development of replicating viral vectors for gene therapy is the lack of tools to monitor viral gene expression and replication in vivo. In the case of MV, this problem has recently been overcome by the development of recombinants that express soluble marker peptides [43]. These viruses possess an additional transcription

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unit upstream of the first gene that encodes either shCEA (MV-CEA) or ␤hCG. These two peptides, cloned in the MV genomic position sustaining highest expression, were selected because they are nonimmunogenic, without relevant biological function, and have a relatively short half-life. Moreover, laboratory tests to measure their serum levels are available in nearly every hospital. Human carcinoembryonic antigen is used as a tumor marker for several types of cancer, whereas ␤hCG is mainly used for the diagnosis of pregnancy and as a tumor marker for certain rare malignancies. When MV encoding the marker genes was inoculated into transgenic mice susceptible to MV-infection because they express human CD46 and have a defective interferon system [40], viral replication could be monitored by measuring the serum or urine levels of the marker peptides. Furthermore, the trackable viruses elucidated the reasons for different MV antitumor effects in murine tumor models. A rapid rise and fall of serum CEA levels after inoculation of MV was typically associated with a good tumor response, whereas low or absent CEA levels indicated a failure of the virus to infect or replicate in the tumor cells. Some tumor cell types were chronically infected and produced progressively rising CEA levels, but the infection did not lead to tumor regression. Measles virus CEA also recently showed significant oncolytic effects in subcutaneous and intracranial orthotopic mouse models of human glioblastoma [52]. Trackable MV hopefully will allow monitoring of viral replication in clinical trials: It should be possible to correlate marker peptides levels with different doses and routes, with antitumor effects, and with toxicity levels. This will facilitate the development of MV-based virotherapy. MEASLES VIRUS WITH RETARGETED CELL ENTRY A major challenge in the development of vectors for oncolytic virotherapy is the production of viruses that are specific for tumor cells. This specificity can theoretically be conferred to different stages in the viral life cycle: replication, transcription, or cell entry. Certain viruses replicate preferentially in tumor cells naturally, others have been genetically engineered

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to do so [53,54]. A second way to achieve specificity for a given tissue is the use of tissue-specific promoters active only in the targeted cells [55]. The third approach is in principle the most straightforward: to target viral entry, the first step of the viral cycle. Measles virus entry is mediated by two envelope glycoproteins—the attachment protein H and the F protein that executes fusion. Because the attachment and the fusion function are distributed on two entities, retargeting strategies are based on H protein modification only (Fig. 1A, top). Indeed, we showed that the addition of specificity domains to the viral H protein led not only to binding to cells that express the appropriate ligand but also to subsequent entry [56]. The first specificity domains that were shown to promote attachment and entry of MV were epidermal growth factor (EGF) and insulinlike growth factor 1 (IGF-1) [57]. These domains were connected to the extracellular terminus of the viral H via a flexible linker. The hybrid proteins (Fig. 1, top) were stable and were efficiently incorporated in the viral envelope. Measles virus displaying EGF or IGF-1 on their surface efficiently entered rodent cells that expressed the human EGF or IGF-1 receptors and that are normally not permissive for MV infection. Single-chain antibodies (scFv) with any desired specificity can be selected, and therefore the next step was to verify whether a single-chain antibody displayed on H was compatible with virus assembly, and elicited targeted entry [58]. The first scFv displayed on MV H was directed against hCEA, a glycoprotein expressed during embryogenesis and in certain tumors of epithelian origin, including colon carcinoma, pancreatic carcinoma, and some types of lung cancer [59]. Indeed, the anti-hCEA scFv displayed on MV H mediated entry in rodent cells that express human CEA. Subsequently, recombinant viruses with H proteins displaying other scFv in place of standard H were produced. One of these was directed against CD38, a myeloma marker [60], and one against CD20, a common lymphoma antigen [61]. These viruses can also enter cells via the corresponding antigen. These results suggest that MV can probably be retargeted to many of the cell-surface antigens against which scFv are available.

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The viruses described above are still able to infect cells via the two known natural MV receptors, namely CD46 and SLAM. However, several residues in the H protein that are necessary for efficient fusion mediated by one or the other receptor have been identified [62,63]. Moreover, when the genes for these proteins were exchanged for the standard gene in the MV-infectious cDNA, viruses were recovered that enter the cells selectively via SLAM or CD46. Currently, mutations restricting entry through the natural receptors are being combined with specificity domains to obtain fully retargeted viruses that are no longer able to enter cells via their natural receptors.

MEASLES VIRUSES WITH ENHANCED CYTOTOXICITY In the last years, several systems to improve the cytolytic effects of viral vectors in gene therapy of cancer have been developed [64]. The most common approach is the introduction of ‘‘suicide genes’’ into the infected cell [65]. The proteins encoded by these genes transform a normally nontoxic prodrug into a toxic metabolite and thus kill the cell that expresses it. The most widely used suicide gene/prodrug combinations are herpes simplex virus thymidine kinase (HSV-TK)/ganciclovir and Escherichia coli cytosine deaminase/5-fluorocytosine. Both prodrugs are already used in the clinic to treat human cytomegalovirus or fungal infections, respectively. An important advantage of suicide gene therapy is that the toxic metabolite may not only kill the cell in which the suicide gene is expressed, but also the neighboring cells. This phenomenon is called bystander effect. Recently, HSV-TK has been successfully introduced into the genomes of simian virus 5, another member of the Paramyxoviridae [66], and vesicular stomatitis virus, a rhabdovirus [67]. Recombinant MV expressing different suicide genes have also been rescued, and the therapeutic effect of these genes in mouse cancer models is currently under investigation (Springfeld and Cattaneo, unpublished data).

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An alternative to the ‘‘classical’’ suicide genes mentioned above is the sodium-iodine symporter (NIS) gene, a gene that is normally expressed in the thyroid [68]. The gene product, a large transmembrane glycoprotein in the basolateral membrane of the thyroid follicular cells, is responsible for the transport of iodine into the thyroid, where it is subsequently incorporated in the thyroid hormones. The concentration of iodine in the thyroid tissue by NIS is also the basis for diagnostic thyroid scintigraphy and, more importantly, the treatment of malignant and benign thyroid disorders with radioactive iodine. The treatment option with iodine-131 results in remarkably good prognosis of patients even with metastasized follicular and papillary thyroid cancer [69]. Different groups introduced the NIS gene into several tumor cell lines and showed that these cell lines could be sensitized to the treatment with iodine-131 [70–72]. A recombinant MV expressing NIS (MV-NIS) has been rescued, and intratumoral spread of this virus in myeloma xenografts could be demonstrated by serial gamma-camera imaging of iodine-123 uptake. Furthermore, MM1 myeloma xenografts resistant to MV-NIS treatment alone completely regressed after administration of iodine-131 nine days after a single intravenous injection of MV-NIS [73]. PERSPECTIVES Cancer is the second-leading cause of death in industrialized countries, and the available therapies–mainly surgery, radiotherapy, and chemotherapy–can cure only a minority of patients. Treatment with replicating oncolytic viruses is a promising new approach to add to the armamentarium of cancer therapies [74]. Among the different viruses that are being developed for oncolytic therapy, MV has several distinctive properties. First, the vaccine strain has an excellent safety record and has been administered without major complications to millions of people. Second, because MV is a human virus with known pathogenicity, there is no risk of transforming an animal virus into a human pathogen, a possible concern

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with animal viruses. Third, MV has an inherent oncolytic potential, as suggested by several case reports of regression of human tumors after natural MV infections and recently confirmed in animal models. Fourth, the well-established MV reverse genetics system, in combination with the minimal constraints on MV particle structure, have favored the development of several avenues of experimentation, leading to the enhancement of the natural oncolytic properties. Experimental approaches include the introduction of suicide genes to enhance virus cytotoxicity, or of immunomodulatory genes to enhance the response against tumor cells. Also fascinating is the unique possibility to retarget MV by scFv to specific tumor antigens. Up to now, scFv have been shown to efficiently mediate viral entry through a targeted receptor only when displayed on MV; similar experiments with adenoviruses have been confronted with the constraints on viral assembly imposed by the icosahedral symmetry of the capsid. In retroviruses, the concentration of attachment and fusion function in a single protein complicates retargeting. A major obstacle to the usage of MV and many other viruses for virotherapy of cancer is the presence of neutralizing antibodies in the majority of patients. However, there is evidence that a subclinical measles infection is possible even in seropositive individuals [75–77]. The oncolytic effects of reovirus [78], adenoviruses [79], and herpes viruses [80] were not eliminated by pre-existing antibodies when the viruses were inoculated intratumorally. Several approaches to diminish the patient immune response against viral vectors have been tested recently. A study with replicating reovirus showed that the oncolytic effect of reovirus therapy in a murine model was abolished in the presence of neutralizing antibodies. However, it was restored when the animals where treated with cyclosporin or anti-CD4/CD8 antibodies [81]. It is also possible to exchange the MV envelope proteins with the homologous proteins of related animal viruses, an approach already taken with canine distemper virus, another Morbillivirus (von Messling and Cattaneo, unpublished). However, CDV induces crossreactive antibodies to MV. Tupaia paramyxovirus is a nonpathogenic virus that is not neutral-

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65. Springer CJ, Niculescu-Duvaz I. Prodrug-activating systems in suicide gene therapy. J Clin Invest 2000; 105:116–1167. 66. Parks GD, Young VA, Koumenis C, Wansley EK, Layer JL, Cooke KM. Controlled cell killing by a recombinant nonsegmented negative-strand RNA virus. Virology 2002; 293: 192–203. 67. Fernandez M, Porosnicu M, Markovic D, Barber GN. Genetically engineered vesicular stomatitis virus in gene therapy: application for treatment of malignant disease. J Virol 2002; 76: 895–904. 68. Spitzweg C, Morris JC. The sodium iodide symporter: its pathophysiological and therapeutic implications. Clin Endocrinol (Oxf) 2002; 57:559–574. 69. Schlumberger MJ. Papillary and follicular thyroid carcinoma. N Engl J Med 1998; 338:297–306. 70. Mandell RB, Mandell LZ, Link CJ, Jr. Radioisotope concentrator gene therapy using the sodium/iodide symporter gene. Cancer Res 1999; 59:661–668. 71. Cho JY, Shen DH, Yang W, Williams B, Buckwalter TL, La Perle KM, Hinkle G, Pozderac R, Kloos R, Nagaraja HN, Barth RF, Jhiang SM. In vivo imaging and radioiodine therapy following sodium iodide symporter gene transfer in animal model of intracerebral gliomas. Gene Ther 2002; 9:1139–1145. 72. Boland A, Ricard M, Opolon P, Bidart JM, Yeh P, Filetti S, Schlumberger M, Perricaudet M. Adenovirus-mediated transfer of the thyroid sodium/iodide symporter gene into tumors for a targeted radiotherapy. Cancer Res 2000; 60:3484–3492. 73. Dingli D, Peng KW, Harvey ME, Greipp PR, O’Connor MK, Cattaneo R, Morris JC, Russell SJ. Image-guided radiovirotherapy for multiple myeloma using a recombinant measles virus expressing the thyroidal sodium iodide symporter. Blood 2004; 103:1641–1646. 74. Russell SJ. RNA viruses as virotherapy agents. Cancer Gene Ther 2002; 9:961–966. 75. Pedersen IR, Mordhorst CH, Glikmann G, von Magnus H. Subclinical measles infection in vaccinated seropositive individuals in arctic Greenland. Vaccine 1989; 7:345–348.

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76. Muller CP, Huiss S, Schneider F. Secondary immune responses in parents of children with recent measles. Lancet 1996; 348: 1379–1380. 77. Damien B, Huiss S, Schneider F, Muller CP. Estimated susceptibility to asymptomatic secondary immune response against measles in late convalescent and vaccinated persons. J Med Virol 1998; 56:85–90. 78. Coffey MC, Strong JE, Forsyth PA, Lee PW. Reovirus therapy of tumors with activated Ras pathway. Science 1998; 282: 1332–1334. 79. Heise C, Kirn DH. Replication-selective adenoviruses as oncolytic agents. J Clin Invest 2000; 105:847–851. 80. Todo T, Rabkin SD, Sundaresan P, Wu A, Meehan KR, Herscowitz HB, Martuza RL. Systemic antitumor immunity in experimental brain tumor therapy using a multimutated, replication-competent herpes simplex virus. Hum Gene Ther 1999; 10: 2741–2755. 81. Hirasawa K, Nishikawa SG, Norman KL, Coffey MC, Thompson BG, Yoon CS, Waisman DM, Lee PW. Systemic reovirus therapy of metastatic cancer in immune-competent mice. Cancer Res 2003; 63:348–353. 82. Tidona CA, Kurz HW, Gelderblom HR, Darai G. Isolation and molecular characterization of a novel cytopathogenic paramyxovirus from tree shrews. Virology 1999; 258:425–434.

4 Antitumor Immune Memory and its Activation for Control of Residual Tumor Cells and Improvement of Patient Survival A NEW CONCEPT DERIVED FROM TRANSLATIONAL RESEARCH WITH THE VIRUSMODIFIED TUMOR VACCINE ATV-NDV

VOLKER SCHIRRMACHER Division of Cellular Immunology, Tumor Immunology Program, German Cancer Research Center (DKFZ) Heidelberg, Germany

SUMMARY A new concept is presented that proposes that a certain threshold of antitumor immune memory plays an important role [1] 481

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in the control of residual tumor cells that remain after most therapies and [2] for long-term survival of treated cancer patients. This immune memory is T cell based and most likely maintained by persisting tumor-associated antigen (TAA) from residual dormant tumor cells. Such immune memory was prominent in the bone marrow in animal tumor models as well as in cancer patients. Pre-existing antitumor memory T cells from cancer patients could be activated by stimulation with TAA-pulsed autologous dendritic cells (DC) or with virusinfected TAA expressing autologous tumor cell vaccine (ATVNDV). Antitumor vaccination with ATV-NDV caused augmentation of antitumor memory Delayed Hyper-sensitivity (DTH) responses. In a variety of Phase II vaccination studies, an optimal formulation of this vaccine could improve long-term survival beyond what is seen in conventional standard therapies. Possible reasons for differences in long-term survival of patients treated by immunotherapy vs. chemotherapy are being discussed. INTRODUCTION The host immune response to foreign challenge requires the coordinated action of both the innate and acquired arms of the immune system. The innate immune response not only provides the first line of defense against microorganisms but also the biological context–the ‘‘danger signal’’–that instructs the adaptive immune system to mount a response [1]. The adaptive response is mediated by T and B lymphocytes that have undergone germline gene rearrangements of their antigen-specific receptors. This second line of defense is characterized by exquisite specificity and long-lasting memory. In innate immune responses, Toll-like receptors (TLR) [2] function as pattern-recognition receptors and allow the recognition of microbial components for activation of the immune system. Activation of TLR leads to the release of several inflammatory mediators, including chemokines from resident tissue-macrophages and DCs and modulates the expression of chemokine receptors on DCs. These TLR-mediated events are essential for both the recruitment of immature DCs to sites of

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pathogen entry and their ultimate journey back to lymph nodes to activate naı¨ve T cells. In addition, chemokines released by resident tissue cells after TLR activation guide these activated T cells into the site of pathogen entry or replication. In this way, chemokines link innate immune cell activation in the tissue to the recruitment of antigen-specific T cells generated in secondary lymphoid organs [3]. In this Chapter, I review our work and concepts related to the immunotherapy of cancer. We exploit the use of virus infection to introduce danger signals into tumor cells to activate, via antitumor vaccination, innate immune responses and adaptive antitumor immune responses in connection with long-term immunological memory. The review includes a summary of results from many clinical studies. The survival data are interpreted to result from activation and maintenance of long-term immune memory. DEVELOPMENT OF THE NEW CONCEPT IN ANIMAL TUMOR MODELS Postoperative Active-Specific Immunotherapy in the ESb Tumor Model About 20 years ago, we started this work in the murine ESb lymphoma animal tumor model. The ESb lymphoma is one of the most aggressive animal tumors. It metastasizes to visceral organs, in particular, the liver, and kills syngeneic hosts within about 12 days. We used it as a challenge to design new antimetastatic therapy strategies. Treatment with cytostatic drugs that were claimed to have antimetastatic activity were not effective and even reduced the overall survival time. In contrast, postoperative vaccination with a virus-modified— but not with unmodified—ESb cells was able to cause protection from metastases in about 50% of syngeneic mice [4]. The surviving animals developed long-lasting protective immunity specific for the ESb tumor line and did not cross-react with other syngeneic or allogeneic tumor lines. It was based on tumor-specific immune T cell memory. The effectiveness of this approach of postoperative active specific immunotherapy (ASI) with virus-modified autologous

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live cell tumor vaccine was thereafter confirmed in other metastasising animal tumors such as murine B16 melanoma [5], 3LL Lewis lung carcinoma [6], and guinea pig L10 hepatocarcinoma [7,8]. The Trick of Virus Infection Using Newcastle Disease Virus In those studies, we had selected for the purpose of virus infection an avian RNA paramyxovirus, Newcastle disease virus (NDV). Because this was a good choice, we continued to use NDV for clinical application. Newcastle disease virus is an enveloped virus of 150 nm to 300 nm size containing a nonsegmented negative-stranded RNA of 15 kb size (Figure 1A). Virulent strains of NDV are important pathogens for poultry and are widely distributed in naturally occurring bird populations. The NDV genome contains six genes encoding for the following six gene products listed in order from the 3′- end: nucleocapsid protein (NP, 55 kD); phosphorprotein (P, 53 kD); matrix protein (M, 40 kD); fusion protein (F, 67 kD); hemagglutininneuraminidase (HN, 74 kD); and large protein (L, 200 kD). The F glycoprotein is synthesized as an inactive precursor (Fo, 67 kD), which undergoes proteolytic cleavage to yield the biologically active protein consisting of the disulfide-linked chains F1 (55 kD) and F2 (12.5 kD) [9]. Upon accidental exposure, NDV can also infect humans. Human infections are mild and can cause symptoms of conjunctivitis or laryngitis. There is an extensive safety database for NDV, primarily from low-dose human tumor vaccine trials. Newcastle disease virus is well tolerated in humans in doses of at least 3 ⳯ 109 infectious units by the i.v. route and at least 4 ⳯ 1012 infectious units by the intratumoral route. Complementing these clinical findings, animal safety data provide evidence of the low pathogenicity of NDV in mammals [10]. An Effective Method of Introducing Danger Signals into Tumor Cells Figure 1 illustrates the structure of NDV, its surface molecules HN and F (A), and the two steps of infection, namely [1] cell surface binding and [2] replication in the cells’ cytoplasm (B).


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Figure 1 (A) Structure: Newcastle disease virus is an avian paramyxovirus of 150 nm to 300 nm diameter with an envelop containing two surface proteins (HN and F). Its 15-Kb nonsegmented genome contains six genes, two of which code for the surface proteins HN and F. (B) Replication of NDV in tumor cells. [1] Initial binding to a host cell takes place through interaction of HN in the virus coat with sialic acid expressing cellular HN receptors (gangliosides). Infectious virus from the allantoic fluid of infected embryonated eggs express an active fusion protein F, which, upon interaction with HN and HN receptors will cause virus–host cell membrane fusion. This allows the viral genome to enter the cytoplasm of the host cell. Normal cells resist virus replication but tumor cells do not [11]. Virus replication in tumor cells leads to expression of a high density of surface HN and F molecules. The avirulent strain Ulster performs an abortive monocyclic replication cycle [36] within 6 to 40 hours, upon which noninfectious virus progeny is produced before the tumor cells die via apoptosis [12,16]

Newcastle disease virus can replicate up to 10,000 times better in human cancer cells than in most normal human cells. This finding has prompted much interest in this virus as a potential anticancer agent. The resistance of normal cells to infection by Newcastle Disease Virus (NDV) may have to do

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with their strong interferon (IFN) ␣ response. Whereas normal peripheral blood mononuclear cells (PBMC) produce IFN␣ immediately after surface contact with inactivated NDV, tumor cells produce IFN␣ only after true virus infection. Interferon␣ is an antiviral factor that can quickly induce a state of virus resistance in other cells. Newcastle disease virus has been labelled as a complementary and alternative medicine (CAM) and much detailed information can be found at a related homepage of the National Cancer Institute USA (http:// www.nci.nih.gov/cancerinfo/pdq/cam/NDV). The first hints of the potential anticancer benefit of this virus were noted more than 30 years ago. Three different conceptual uses of NDV in cancer treatment can be distinguished: [1] Use for tumor-selective cytolysis (oncolysis) [10], [2] use of NDV as an adjuvant and danger signal in a tumor vaccine for stimulation of cytotoxic T lymphocyte (CTL) and DTH responses after tumor vaccination [11], [3] use of NDV for nonspecific immune stimulation and induction of cytokines and IFNs [8,10]. As a consequence of infection of tumor cells by NDV, tumor cells can be perceived by the immune system as ‘‘dangerous’’ because of the following danger-signalling molecules that we have identified: [1] viral HN-molecules [12,13], [2] doublestrand RNA [14], [3] IFN-␣[??]␤, [13,15], [4] chemokines (RANTES and IP-10) [16]. (Figure 2.) The release of large amounts of IFN-␣ by natural IFNproducing cells (NIPC) and plasmacytoid DCs indicates that these cells of the innate immune system have sensed ‘‘danger.’’ It has only recently become clear that IFN-␣ has an important adjuvant function in the immune response [17]. It activates DCs [18] and induces TRAIL in NK cells [19] and the interleukin (IL)-12– receptor ␤ chain in T cells [20]. Together with IL-12, IFN-␣ polarizes the T cell toward a cell-mediated Th1 response characterized by DTH and CTL activity. In addition, IFN-␣ induces the upregulation of molecules important for antigen recognition (e.g., human leukocite antigen)(16), cell–cell interaction (e.g., cell adhesion molecules)[16], and cytotoxicity (e.g., TRAIL)[13].


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Figure 2 Mechanisms involved in the enhanced antitumoral immune response when tumor cells are infected with Newcastle disease virus (NDV): (1) Upregulation of major histocompatibility complex molecules, ICAM-1 (CD54) and LFA-3 (CD58), and an increase in co-stimulation [16]. (2,3) Delivery of danger signals through surface protein HN [13] and double-strand RNA [14]. Transfectants expressing HN induce high amounts of interferon (IFN)-␣ in human peripheral blood mononuclear cells [13]. Responsible for this response is a subset of CD16Ⳮ/CD64Ⳮ cells belonging to the innate immunity system [13,15]. Similar IFN-␣ responses can be induced by dsRNA via Toll-like receptor 3 in plasmacytoid dendritic cells [14]. Interferon␣ and ␤ activate a variety of additional molecules, including heatshock proteins (HSP) and tumor necrosis factor-related apoptosisinducing ligand [13,15,41]. [4] Apoptotic bodies and lysate from NDV-infected tumor cells are taken up by immature dendritic cells and cause their activation for augmented stimulation of antitumor memory T cell responses in Enzyme-Linked-Immuno-Spot (ELISPOT) assays [52]. (5) Infected tumor cells release the chemotactic factors regulated upon activation normal T cell expressed and secreted (RANTES) and IFN-␥–inducible protein-10 (IP-10), which contribute to augmented recruitment of monocytes and T cells [16]. (6) Released noninfectious NDV progeny can directly activate monocytes and macrophages to cytotoxic antitumoral activities [41]

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Lessons from Tumor Dormancy Studies As already mentioned, postoperative vaccination in the murine ESb tumor model with ESb-NDV vaccine resulted in about 50 % long-term survivors who had established systemic and tumor-specific immune memory [21]. A detailed analysis later revealed the existence of residual tumor cells in such mice in the bone marrow. These cells were never completely eradicated and were kept under immune control at a low level. Therapeutic antitumor vaccination in these animals had thereby caused the establishment not only of immunological memory but also of tumor dormancy. This was confirmed in prophylactic immunization experiments. In immunocompetent animals, we saw a correlation between the persistence of dormant tumor cells at low levels in the bone marrow and long-term protective immune memory [22]. We could break the status of tumor dormancy in situ by CD8 T cell depletion [23]. In immunocompetent tumor-dormant mice, 21% of the bone marrow-derived tumor cells were positive for the proliferation marker Ki67. The fraction of Ki67-positive tumor cells in diseased bone marrow of immune compromised mice was 40% and, in absence of immune CD8 T cells, the frequency of bone marrow-residing tumor cells increased by two orders of magnitude. These findings suggested that tumor dormancy in this model was attributable to active immune control of tumor cells by CD8 T cells in the bone marrow, keeping them at a low level without elimination [24]. Tumor dormancy in general and in clinical cancer in particular can be caused by different growth constrain mechanisms [24]. One involves macrometastatic lesions that fail to induce angiogenic activity necessary for their expansion. Local hypoxia and undernourishment are insufficient to eradicate the cells but limit their expansion by inducing apoptotic death. Angiogenesis inhibitors such as angiostatin and endostatin can keep small tumor foci dormant over extended periods of time. Another form of tumor dormancy consists of solitary cancerous cells that reside after operation of the primary tumor at distinct sites such as bone marrow or other tissues.


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An Interactive Balance Between Residual Tumor Cells and Immune Memory In our animal tumor studies, we noticed an interactive balance between residual tumor cells and immune memory [24]. Persistence of tumor cells and, therefore, persistence of TAA derived from them correlated with long-term protective immune memory [22–24]. Following injection of live or irradiated tumor cells into the external ear pinna in exemplum (i.e.) of mice—a site where the tumor cells could not grow—comparable numbers of X-Gal–stained cells were detectable in the bone marrow of host animals one week after inoculation. Live tumor cells persisted at a similar level (about 30 cells/106 bone marrow cells) in the bone marrow for follow-up periods of up to 2 months, while the number of bone marrow-derived irradiated cells declined within 3 weeks. The persistence or nonpersistence of tumor cells in bone marrow seen with injection of either live or irradiated tumor cells correlated with the presence or absence of long-term memory in these respective groups. Thus, when the tumor challenge was made later than 4 weeks after vaccination, only the live tumor vaccine could effectively protect the mice. The tumor-dormant mice were fully protected even when challenged with parental tumor cells 6 months after primary i.e. tumor cell injection. Characteristics of Memory T Cells Whereas naı¨ve T cells can only be primed by antigens that are cross-presented by professional host antigen-presenting cells such as DCs, memory T cells can also be activated directly by a tumor vaccine presenting TAA together with costimulatory signals. Secondary immune responses by memory T cells are faster and stronger than primary responses. Their requirements for activation are less strict (lower dependency on costimulation) and they release a broader spectrum of cytokines and are multifunctional after re-activation [25]. Thus, memory T cells are superior to naı¨ve T cells [26] for protective immunity. There is a programmed development of effector and memory CD8 T cells, and different subsets of memory T cells, namely ‘‘central’’ and ‘‘effector’’ memory cells, have recently been distinguished. Of special interest are also stem cell-like

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Table 1 Stem Cell-like Properties of Memory T Cells 1. Self-renewal capacity Response to homeostatic signals; causing self-renewal 2. Programmed differentiation Response to antigen-presenting cells; stimulating naive T cells to differentiate to effector cytotoxic T lymphocytes and, finally, to memory T cells 3. Pluripotentiality Response to antigen; activating perforin, granzymes, IFN-␥, IL-2, etc. 4. Longevity/immortality unlimited proliferation; via telomerase upregulation (?) (From Ref. 25,26.)

properties of memory T cells: Upon response to homeostatic signals they have a self-renewal capacity [26]. Longevity or immortality is another important aspect of memory T cells, which may involve telomerase upregulation (Table 1). We recently established a novel tumor model system for the study of long-term protective immunity and immune T cell memory [27]. In this adoptive memory T cell transfer system involving as recipients nude (nu/nu) mice, we were able to study [1] the role of persisting antigen for long-term maintenance of peptide epitope-specific CD8 memory T cells and [2] the longevity of the cells. FROM MOUSE TO MAN Long-term persistence of tumor cells in a dormant state is suggested also from clinical observations in cancer patients, notably breast cancer [28]. Some patients develop secondary tumors at distant sites many years after successful therapy of the primary tumors; others do not develop recurrencies in spite of disseminated tumor cells at the time of diagnosis. The longest duration of breast cancer dormancy—i.e., the longest interval between primary treatment and tumor recurrence—was calculated in a retrospective study involving 1547 patients, to be between 20 and 25 years [28]. In breast cancer, 25% to 43 % of primary-operated patients exhibit micrometastatic tumor


491

cells in their bone marrow. Detection levels are in the range of 1 to 10 cancer cells per 106 to 107 bone marrow-derived mononuclear cells. Successful enrichment, reliable identification, and molecular profiling are key issues of ongoing and future studies [29]. Antitumor Memory T Cells in Cancer Patients To test for the presence of memory T cells in cancer patients, we investigated bone marrow of breast cancer patients with respect to tumor cell content, immune activation status, and memory T cell content [30]. Bone marrow-derived cells from primary-operated breast cancer patients (n ⳱ 90) were compared with those from healthy donors (n ⳱ 10) and cells from respective blood samples. Cytokeratine 19-positive tumor cells were detected by nested polymerase chain reaction. Threecolor flow cytometry was used to identify numbers and activation state of T cells, natural killer (NK) cells, monocytes/ macrophages, and subsets by a panel of monoclonal antibodies. The proportion of memory T cells among the CD4 and CD8 T cells was found to be much higher in bone marrow of cancer patients than in healthy donors (p ⬍ 0.001). The extent of memory T cell increase was related to the size of the primary tumor. The highest relative memory content was detected in patients with T2 tumor stage and these were significantly different from patients both with T1 and T3/4 stages. Thus, with tumor progression, the memory content in T cell populations first steadily increased and then decreased again. Patients with disseminated tumor cells in their bone marrow had more memory CD4 T cells than patients with tumor cell negative bone marrow [30]. Our proposition from animal studies that bone marrow is a special compartment for immunological memory and tumor dormancy [22] had therefore been supported by our clinical findings. Therapy of Human Tumors in NOD/SCID Mice with Autologous Memory T cells Further functional studies with patients’ bone marrow-derived memory T cells revealed tumor specificity and functional

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competence [31]. We could demonstrate the existence of TAAspecific CD8 T cells that specifically bound to tetramers consisting of human leukocyte antigen (HLA)-A2 molecules and peptides derived from two important markers of breast cancer, namely MUC-1, a mucin-type TAA, and HER2/neu, an overexpressed growth-factor receptor. Bone marrow memory T cells from patients could be specifically restimulated in short-term culture (20 to 40 hours) to IFN-␥–producing cells by autologous DCs pulsed with respective tumor lysate or with the aforementoned TAA. The calculated frequency of memory T cells in Enzyme-Linked Immuno-Spot (ELISPOT) among total T lymphocytes from bone marrow of patients responding to autologous TAA was rather high and varied from 1/200 to 1/11000. We could also induce antitumor CTL activity in re-activated bone marrow-derived memory T cells. Their immunotherapeutic competence in vivo was finally demonstrated by showing regression of human breast cancer in non-obese diabetes mellitus/severe combined immuno-deficiency (NOD/SCID) mice after transfer of autologous reactivated bonemarrow-derived memory T cells [31]. Following such cell transfer, human T cells were found to infiltrate the human breast cancer tissue (Fig. 3). Most infiltrating T cells had the memory marker CD45 R0. CD8 T cells were found in close contact with CD4 T cells and within the tumor close to necrotic areas, where, in serial tumor sections, apoptotic cells could be detected [31]. Tolerance to Tumor-Associated Antigens In some of the cancer patients investigated, it was possible to perform a paired analysis of samples from peripheral blood (PB) and bone marrow. In all these cases, the T cells from the blood were negative and did not produce a significant ELISPOT response, whereas the bone marrow samples were positive. Because tetramer analysis had shown the presence of TAA-specific T cells in PB of breast cancer patients with a frequency similar to that in bone marrow samples, these data suggested that the PB-derived T cells were tolerant (anergic) and not functional [31].


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Figure 3 Tumor infiltration (A) and therapy of human breast carcinoma (B) in non obese diabetes mellitus/severe combined immunodeficiency (NOD/SCID) mice by ex vivo re-activated patient derived memory T cells from bone marrow [31]. (A) Tumor cells are stained by mAb to Mucin-1 (MUC) and T cells by mAb anti CD3. Notice that there are no tumor infiltrating T cells in control mice (b) which were either untreated (䊏) or treated with T cells from peripheral blood mononuclear cells (⌫), while blood marrow-derived T cells infiltrated the tumor (a) and caused graft-vs.-tumor reactivity, leading to complete tumor remission (group ⌬ in B)

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Newcastle Disease Virus Infection Breaking Tolerance to Tumor-Associated Antigens Tumor immunologists have developed a number of strategies to overcome states of anergy or tolerance to TAA. Some used TAA expressed in xenogeneic cells; others tried to xenogenize the tumor cells or to use xenogeneic DNA immunization or recombinant viruses expressing TAA. In cases of non-identified TAA, it is also possible to use whole-cell tumor vaccines, typically transfected with cytokines, costimulatory molecules, or infected with viruses, and to use them in combination with exogenous cytokines. We could demonstrate in an autologous human anti-melanoma CD4 T helper clone that infection by NDV of autologous melanoma cells induces a T cell costimulatory activity and thereby prevents, in the clone, the induction of anergy by the tumor cell [32]. Without NDV infection, contact with autologous melanoma cells rendered the clone nonreactive and unresponsive even to subsequent stimulation by IL-2. Newcastle disease virus-infection of the melanoma cell line not only completely restored the proliferative response of the tumorspecific T cell clone but also inhibited the induction of anergy. Electrophoretic mobility shift assays of cell lysates from the clone revealed the induction of the CD28-responsive complex by co-incubation with NDV-infected melanoma cells [32]. Conditioning the Immune System to Associate Recognition of Tumor-Associated Antigen with Danger Based on results of conditioning experiments with immune responses in animal models [33,34] we propose that it might be possible to condition or train the immune system to associate recognition of TAA with danger signals. Training could be performed by repeated vaccination with vaccine expressing TAA and danger signals. We also conclude that NDV is an appropriate reagent to introduce danger signals into tumor cells. Finally, we hypothesize that once the immune system’s memory T cells are trained to associate TAA recognition with danger [1], they may not require the danger signal any longer and can react to TAA without being tolerized.


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CLINICAL IMMUNOTHERAPY STUDIES Since 1986, when we first reported on the ‘‘prevention of metastatic spread by postoperative immunotherapy with virally modified autologous tumor cells’ [4], it took about 10 years of translational research to develop the autologous human tumor vaccine ATV-NDV and to perform ‘‘proof of principle’’ clinical studies at the evidence level of Phase II [35]. This pioneering translational research was everything but easy. It meant entering new, ‘‘forbidden’’ territory. In addition, the scientific community was not prepared for constructive discussion of these new thoughts and approaches. It took a lot of courage, self-confidence, and energy on the part of myself and cooperating clinicians to circumvent the various road blocks that were thrown on our way and to try to continue, mostly without financial or other support. Development of an Autologous Virus Modified Tumor Vaccine for clinical studies The specific component of each vaccine for human application that we developed in analogy to the effective animal tumor vaccine are patient-derived (autologous) live tumor cells (ATV). These are infected by the avirulent strain Ulster of NDV and inactivated by 200 Gy ␥-irradiation to produce the vaccine ATV-NDV. Tumor cells are isolated from freshly operated tumor specimens by mechanical dissection and enzymatic dissociation and can be stored, after controlled freezing in liquid nitrogen. Although the first clinical studies employed total dissociated cells from a tumor, we later introduced a further tumor cell purification procedure to remove tumor infiltrating lymphocytes by immunomagnetic beads [35]. In some other studies, cell culture-adapted autologous tumor cells were used instead. All studies were approved in advance by local ethical commissions. We selected the non-lytic strain Ulster for reasons of safety during application in cancer patients and because we intended to develop a virus-infected whole-cell cancer vaccine consisting of intact viable irradiated cancer cells. Newcastle disease virus Ulster has a monocyclic abortive replication cycle in tumor cells [36]. This replication involves the formation of

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double-strand RNA that functions as a danger signal and activates Toll-like receptors [14]. In this way, we tried to link the expression of TAA with danger signals [1,37]. We decided to use autologous tumor cells because we had experienced that protective antitumor immunity in animal tumor models was highly specific for the autologous tumor and also because autologous tumor cells represent the closest possible match to a patient’s tumor. Autologous tumor cells might express not only common TAA but also individually unique TAA derived from mutations or other genetic alterations. The use of whole tumor cells eliminates the need to first identify the respective TAA. It has been the experience of many tumor immunologists that whole-cell vaccines can stimulate the immune system more efficiently than oncolysates [38]. Tumor cell membrane integrity was found to be important for CTL activation by cancer vaccines [39]. Newcastle disease virus Ulster is first adsorbed to the tumor cells in vitro (1-hour binding) (Fig. 1). Then the virus-modified tumor vaccine is injected intradermally, allowing for virus replication in vivo at the site of vaccine application. Vaccine consisting of tumor cells infected with NDV Ulster should remain in the body long enough to generate effective immune responses that are mainly based on T cell-mediated immunity. Viral replication in the tumor cells takes about 6 to 40 hours [10–2], a time sufficient to generate delayed-type hypersensitivity (DTH) skin responses which are dependent on antigen-specific memory T cells. During this time period of 6 to 40 hours after vaccine application, the infected tumor cells can produce progeny NDV virus particles. Although these are noninfectious because of uncleaved Fo molecules, they are able to stimulate innate immune responses in NIPC [15,13] and monocytes that are recruited by IP-10 (Fig. 2). The release of interferon-␣ and other cytokines causes activation of various antitumor effector cells such as NK cells and cytotoxic monocytes/macrophages [40,41]. In this way, we may achieve a link between innate and adaptive immune responses. Figure 2 illustrates the consequences of human tumor cell infection by NDV Ulster for the immune response. We found


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that modification with live, but not inactive, NDV induced, in all human tumor cells tested, the production of IFN-␤, IFN-␣, and the chemokines RANTES and IFN-␥–inducible protein 10 (IP-10) [16]. In addition, infection by live NDV induced upregulation of HLA-ABC molecules on all tumor lines tested and HLA-DR molecules on breast carcinoma lines. Two cell adhesion molecules, ICAM-1 (CD54) and LFA-3 (CD58), were also upregulated on human tumor cells after infection with live NDV. Forty-eight to seventy-two hours after infection of the irradiated tumor cells with live NDV, many tumor cells were dead or in early or late stages of apoptosis [16]. Figure 2 illustrates six different mechanisms through which NDV infection of tumor cells leads to greater immunogenicity and enhanced immune responses. Phase I Clinical Studies: Optimization of Vaccine Composition Much of this pioneering work of establishing a human NDV modified tumor vaccine was performed by my clinical colleague T. Ahlert, who now has more than 10 years of experience with the vaccine preparation and application in cancer patients (http://www.biotech-praxislab.de). After having optimized a technical procedure for isolating live tumor cells from fresh operation specimens and having calculated average yields and stability parameters [42], we started to perform Phase I clinical studies [43,44]. In the ESb animal tumor model, we had described before that an optimal vaccine composition that yielded 50% survival benefit after a single inoculation was composed of 107 irradiated tumor cells infected by 32 hemagglutinating units (HU) of NDV Ulster. The first systematic optimization studies for the vaccine ATVNDV were performed in breast carcinoma [44], colorectal carcinoma [45–48], and renal cell carcinoma [49,50] (Table 2). Two to three weeks after tumor operation, we applied, intradermally at the upper thigh at different sites, vaccine composed of different numbers of tumor cells and different doses of virus, as indicated in Table 1. Twenty-four to forty-eight hours later, the local skin reactions to the vaccine were measured by determining the mean diameter of induration. As can be seen from the results of Table 2, optimal skin reactions were observed

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Table 2 Phase I Optimization Studies for the Vaccine ATV-NDV (Dose-Response Relationship) Vaccine composition

Tumor type renal cell carcinoma ′′ ′ ′′ ′′ colorectal carcinoma ′′ ′′ ′′ ′′ ′′ ′′ ′′ ′′

% responder

Virus

Dose (HU)

Mean skin reactivity1 (mm diameter)

Renal carcinoma (n⫽20)

1⫻107 ′′ ′′ ′′

– NDV ′′ ′′

– 8 16 32

4.5 5.8 7.5* 11.0*

90

1⫻107 ′′ ′′ ′′ 2⫻107 2⫻106 ′′ ′′

— NDV ′′ ′′ ′′ ′′ ′′ ′′

— 4 32 64 32 4 32 64

3.0 4.0 7.0* 6.5 6.5 3.0 4.5 4.5

Cell number

Colorectal carcinoma (n⫽20)

67 85 60 50 50 67 67

* p ⬍ 0.05; optimal skin responses to the vaccine were observed in both studies and tumor types (45–50) with 1⫻107 tumor cells infected with 32 HU NDV Ulster. n ⫽ number of patients.

1)

in both studies with 1X107 tumor cells infected with 32 HU NDV Ulster. With this vaccine formulation, 85% of colorectal carcinoma patients and 90% of renal carcinoma patients showed about 7 mm to 11 mm skin indurations at the vaccination site. The fact that the optimal vaccine composition was similar in the ESb mouse tumor model and in cancer patients can perhaps best be explained on the basis of a local memory immune response. Such responses, which are similar to skin responses of allergic people, require only low amounts of antigen. Specificity of Responses Next we evaluated skin responsiveness in patients, not only to the vaccine ATV-NDV but also to autologous tumor cells without virus (ATV) and to various controls. The results in Table 3 show skin reactivities after the first inoculation. It can

NDV – NDV NDV – NDV –

NDV – –

5⫻106 5⫻106 –

1⫻107 1⫻107 – 1⫻107

1⫻107 1⫻107 1⫻107 32 – –

32 – 32 –

32 – 32

32 – 32

Dose (HU)

10.8 4.5 0.0

7.0 4.0 2.0 3.5 0.0

4.5 3.2 0.0

2.6 0.75 0.94

Mean induration (mm diameter)

0

20

10

20

7

9

n

100 90

85 65 15 40 0

100 86 0

89 22 33

% responder

ATV ⫽ tumor cells alone; n ⫽ number of patients; CEA ⫽ carcinoembryonic antigen; HU ⫽ hemagglutinating unit.

NDV – NDV

Virus

5⫻106 5⫻106 –

Cell number

Ref.

49,50

45–48

42–44

42–44

Skin Responsiveness to the Vaccine ATV-NDV, to Tumor Cells Alone, and to Various Controls

breast carcinoma ′′ ATV-NDV ′′ ATV – ovarian carcinoma ′′ ATV-NDV ′′ ATV – colorectal carcinoma ′′ ATV-NDV ′′ ATV – normal colon mucosa CEA 30–60 ␮g renal carcinoma ′′ ATV-NDV ′′ ATV normal kidney epithelium

Cell type

Table 3

Antitumor Immune Memory 499

500

Schirrmacher

be seen that the reactivity to ATV is much smaller, both in terms of mean induration and of percent responder patients. Reactions to the virus alone were either absent or very small. For specificity control of the DTH test, we performed either the Me´rieux test, consisting of several recall antigens, or we used normal cells from either kidney epithelium (in renal carcinoma patients) or from colon-mucosa (in colorectal carcinoma patients), which had to be separated under the same conditions as the tumor cells. In 40% of colorectal carcinoma patients, we saw some reactivity to normal colon mucosa [45,48], whereas in none of the 20 renal carcinoma patients did we detect reactivity to normal kidney epithelium cells [50]. Whether the weak reactivity to normal colon mucosa is attributable to cross-reactions or represents true autoimmune responses remains to be investigated. We thus conclude that DTH responses to TAA can be distinguished from responses to recall antigens and from autoimmune responses. Reactivity to NDV alone was either not seen [42,44] or seen as weak induration in a minority of patients [42–48]. In a separate study, we demonstrated that the recall antigen responses of patients did not correlate with or allow prediction of their responsiveness to autologous tumor cells [48]. It therefore was not a better general immunocompetence that distinguished immunological responder from nonresponder patients. This was recently confirmed with ELISPOT results demonstrating distinct respective memory responses to recall antigens and to TAA in individual patients [51]. The similarity to memory ELISPOT responses suggests a strong involvement of TAA-specific memory cells in the DTH test. With the ELISPOT assay, we also found out that DCs, when pulsed with viral oncolysates from ATV-NDV vaccine, stimulate antitumor memory T cell responses from cancer patients more strongly than when pulsed with tumor lysate [52]. Effects of Repeated Vaccinations We next tested the effect of repeated vaccinations on local skin reactivity to the vaccine ATV-NDV (Table 4). A positive skin response was defined as being more than 2-mm diameter induration. Although in tests of various tumor types [43] we had


501

Table 4 Effect of Repeated Vaccinations on Local Skin Reactivity to the Vaccine ATV-NDV % of patients Various

Colorectal

tumor types* (n ⫽ 27) 1°

3°

PT (n⫽31) 3°

LM (n ⫽ 20) 3°

% Nonresponder (⬍ 2 mm) % Responder

22 77

3 93

100**

100†

Induration intensity: 3–5 mm 5–10 mm 10–20 mm

37 33 7

26 19 48

Carcinoma

n ⫽ number of patients PT ⫽ primary tumor; LM ⫽ liver metastasis * Data from Ref. 43; 1 ° ⫽ first vaccination 3° ⫽ third vaccination. ** Mean diameter of induration and erythema at first vaccination ⫽ 18 mm and at last vaccination 26 mm; 68% of patients showed increased responsiveness. (From Ref. 53.) † Mean diameter induration at first vaccination 8 mm and at last vaccination 9.5 mm. (From Ref. 45,46.)

seen 22% of nonresponders at the first ATV-NDV inoculation, virtually all patients became responders at the third vaccination. This was also true for studies in colorectal carcinoma patients who were vaccinated with vaccine derived either from the primary tumor [53] or from liver metastases [45–48]. There was not only an increase in the percentage of responder patients but also in the induration intensity. Whereas at the first vaccination, patients showed intensities of 3 mm to 5 mm or 5 mm to 10 mm, at the third vaccination, many showed an induration intensity of 10 to 20 mm [53]. Turning Immunological Nonresponders into Responders We were able to induce antitumor DTH reactivity in immunological nonresponders (Table 5). Among 90 cancer patients

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Table 5 Change of Immunological Nonresponders to Responders Following Vaccination with ATV-NDV ATV-NDV Induced DTH Reactivity to ATV in Patients Who Were Negative to ATV at First Test

% of patients n‡

Breast carcinoma*

Colorectal carcinoma with liver metastasis**

Various tumor types†

43 44

9 23

30 23

DTH ⫽ delayed-type hypersensitivity. * (From Ref. 54.) ** In two patients, the reaction increased from 0 to 10 mm and from 0 to 15 mm. (From Ref. 46.) † Melanoma, colon carcinoma, rectum carcinoma, stomach carcinoma, ovarian carcinoma, breast carcinoma, renal cell carcinoma, and acute myeloblastic leukemia. (From Ref. 43.) ‡ n ⫽ number of patients; in total, among 90 patients tested, 31% showed induction of new DTH reactivity (change from nonresponder to responder).

tested who did not react to autologous tumor cells before vaccination, 31% changed from a nonresponder to a responder phenotype after vaccination with ATV-NDV (at least three times) (Table 4). Thus, in these 31% of patients, we were able to induce by vaccination a specific antitumor DTH memory response. Potentiation of Antitumor Memory Responses Next, we investigated the effect of antitumor vaccination with ATV-NDV in original responder patients who already reacted to ATV challenge before vaccination. Table 6 summarizes the results obtained from studies in breast carcinoma [54], ovarian carcinoma [55–56], colorectal carcinoma[45,46,48,53], renal carcinoma [49,50], and other tumor types [43]. Among 264 patients tested, 44% showed significantly increased DTH reactivity to ATV (without NDV) after the course of vaccination. A significant increase in DTH reactivity to ATV was defined by an increase of diameter greater than 3 mm. Thus, in these 44% of patients, we had increased the level of systemic antitumor immune memory reactivity.


503

Table 6 Potentiation of Antitumor Reactivity in Immunological Responders Following Vaccination with ATV-NDV Potentiation of DTH Responses to ATV (Comparison of Last to First Reaction) % of patients with increases ⱖ 3 mm

% of patients n‡

Breast carcinoma

Ovarian carcinoma

46 67

39 18

Colorectal carcinoma* PT LM 57 14

Renal Other tumor carcinoma** types†

42 24

35 20

45 24

DTH ⫽ delayed-type hypersensitivity. * PT ⫽ primary tumor; LM ⫽ liver metastasis. (From Ref. 45–48.) ** In this tumor type, increased DTH reactions were observed only when the tumor vaccine ATV-NDV was supplementedwith interleukin-2. (From Ref. 49,50.) † See legend to Table 4. ‡ n ⫽ number of patients; in total, among 264 patients tested, 44% showed increased DTH reactivity to ATV after vaccination.

Nonresponder Patients The great majority of cancer patients did not show a detrimental response after vaccination [46,54]. This is reassuring and supporting the present strategy of vaccination. The fraction of patients with a decrease was less than 10%. Table 7 shows the fraction of patients who, after vaccination, showed either no change or a decrease of DTH reactivity to autologous tumor cells. Correlation Between Memory Delayed-Type Hypersensitivity Responses and Prognosis A positive correlation between increase in DTH responsiveness to ATV after vaccination and prognosis was seen by us [50,57] and others [59]. A strong increase (⬎5 mm) in antitumor DTH reactivity to tumor challenge after vaccination (in comparison to the first reactivity) predicted a survival advantage (35 vs. 14 months), a correlation that was significant by Wilcoxon test [50]. It has been assumed that such a correlation reflects a better general immunocompetence and therefore better prognosis in this subgroup of patients [60]. This, however,

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Table 7 Fraction of Immunological Nonresponder Patients: No Change or Decrease of DTH Reactivity Following Vaccination with ATV-NDV Colorectal carcinoma**

% of patients with

DTH response*

PT (n⫽14)

LM (n⫽24)

– decrease – no change – increase

7 35 57

8 50 42

Breast carcinoma† (n⫽67)

Ovarian carcinoma† (n⫽18)

4 21

6 22

71

61

* Decrease or increase defined as ⱖ 3 mm. ** PT ⫽ primary tumor, LM ⫽ liver metastasis. (From Ref. 46.) † (From Ref. 54.) n ⫽ number of patients.

is unlikely because we and others did not see a correlation between response to general recall antigens (Me´rieux test) or response to autologous tumor cells [57,59]. Because there was no DTH reactivity to normal kidney epithelial cells, the correlation seen in renal carcinoma patients [50] is likely attributable to activation of specific antitumor immune memory. SIDE EFFECTS The Phase I clinical studies were also performed to evaluate possible side effects. The intradermal vaccinations were well tolerated and could be repeated many times without causing serious problems. A few patients developed mild fever or mild headache for 1 to 2 days. There was no evidence for autoimmune phenomena such as vasculitis, rheumatoid arthritis, or lymphatic disorders [16,45,48,50,61]. Phase II Clinical Vaccination Studies: Evaluation of Efficacy Having seen that antitumor vaccination of cancer patients with ATV-NDV could lead to a significant increase of systemic memory DTH responses to ATV, we next engaged in Phase II


505

clinical vaccination studies to evaluate clinical efficacy of this approach. Table 8 through 11 summarize the most important results from a variety of Phase II studies performed over the past 10 years. Because the majority of studies have been published, I focus here only on the most important aspect—the survival data. Two-Year Survival Table 8 lists the 2-year survival benefits observed in four clinical studies. The survival rate in the group that received postoperative vaccinations with ATV-NDVwas compared to that of nonvaccinated control groups specified in the legend. Two studies were performed in colorectal carcinoma with either locally advanced tumor [53] or with operated solitary liver metastasis [48]. There was about 25% increase of the 2-year survival rate in both studies. Results from a recent study in glioblastoma multiforme [61] revealed a 32% increase of the 2-year survival rate. In a fourth study of patients with recurrent resectable malignant melanoma [8], there was a 20% increase of survival rate in a group of 21 patients. In this study, the comparison was made between a group treated with a vaccine containing at least 3 ⳯ 106 tumor cells and having greater 33% viable cells (b) and another group (a) treated with a vaccine in which both vaccine parameters were below that threshold. This internally controlled study suggests that the observed vaccination effect is not attributable to a placebo effect because both groups were vaccinated. Instead, the better survival was dependent on the dose (⬎3 ⳯ 106 tumor cells) and quality (⬎33% cell viability) of the product. Five-Year Survival Table 9 shows the 5-year survival benefits after postoperative vaccination with ATV-NDV in two studies with [1] locally advanced primary breast cancer [62] and [2] locally advanced colorectal carcinoma [8]. In the latter study, we saw a 25% increase of the 5-year survival rate in a group of 20 patients who received a high-quality ATV-NDV vaccine [8]. In the breast carcinoma study, we saw a 36% increase in the 5-year

(b) solitary liver metastases, RO resectable grade IV

recurrent resectable

(median follow-up 18 months)

Malignant melanoma (n⫽20) 45%

control** (n⫽25) 4% vaccinated† a) ATV-NDV ⬍ 3X106

73.8% control** (n⫽23) 61%

control* (n⫽661)

(n⫽21) 65%

36% vaccinated b) ATV-NDV ⬎ 3X106

vaccinated (n⫽25)

87%

97.9% vaccinated (n⫽23)

vaccinated (n⫽57)

2-Year survival rate

20

32

26

24

% Increase of survival rate

8

61

48

53

Reference

n ⫽ number of patients; * Historic control from the same clinic. ** Pair-matched controls. † This control group was vaccinated with a vaccine containing less than the indicated number of tumor cells and less than 33% cell viability. It is not historic but an actual internal control.


Glioblastoma multiforme (median follow up 36 months)

(a) locally advanced


Colorectal carcinoma

Stage

Two-Year Survival Benefits After Postoperative Vaccination with ATV-NDV

Tumor type

Table 8

506 Schirrmacher

locally advanced

ATV-NDV ⬍1.5⫻106 (n ⫽ 31) 48% ATV-NDV ⬎3⫻106 (n ⫽ 18) 60%

a ATV-NDV ⬍1.5⫻106 (n ⫽ 32) 84% ATV-NDV ⬎3⫻106 (n ⫽ 20) 85%

b

histor. control (n ⫽ 48) 50%

25

36

% Increase of survival rate (b–a)

8

35, 62

Reference

n ⫽ number of patients; a ⫽ group of patients vaccinated with a vaccine containing less than the indicated number of tumor cells and less than 33% cell viability; as in Table 8, this is an actual internal control with an insufficient formulation of the same vaccine; a historic control is included in addition in the colorectal carcinoma study; b ⫽ verum group which received a high-quality formulation of the vaccine.

Colorectal carcinoma

locally advanced

Stage

5-Year survival rate

Five-Year Surival Benefit After Postoperative Vaccination with ATV-NDV

Breast carcinoma

Tumor type

Table 9

Antitumor Immune Memory 507

508

Schirrmacher

survival rate in a group of 33 vaccinated patients in whom the vaccine contained a least 1.5 ⳯ 106 tumor cells and greater than 33% viability [33,62]. Overall Median Survival There was not only a benefit in overall survival as expressed by the percentage of patients surviving for 2 years or 5 years but also when calculating the overall median survival (OS) of the respective whole groups. Table 10 shows the results from two phase II clinical studies. Whereas in the control group of the malignant melanoma study, the OS was 63.6 weeks, in the group vaccinated with a high-quality vaccine, the survival was about twice as long–126 weeks. The median survival prolongation was 62.4 weeks. Similar results can be reported from the recent glioblastoma study. Here the OS in a group of 25 patients vaccinated with a high-quality vaccine was more than twice as long as in a pair-matched control group. Also, the progression free survival was about twice as long as in the control group [61]. Long-Term Survival In four different tumor types for which antitumor vaccinations were performed with ATV-NDV vaccine from autologous Table 10 Benefit in Median Survival

Tumor type

Stage

Malignant melanoma

recurrent, resectable

OS glioblastoma multiforme

IV

PFS (p ⫽ 0.00138) OS (p ⬍ 0.00001)

Median survival (weeks) ATV-NDV* ⬍3⫻106 (n ⫽ 20) 63.6 control (n ⫽ 25) 24 44

ATV-NDV ⬎3⫻106 (n ⫽ 21) 126 ATV-NDV 1⫻107 (n ⫽ 25) 42 92

Median survival prolongation (weeks) Reference

62.4

8

18 48

61

* n ⫽ number of patients; OS ⫽ overall survival; PFS ⫽ progression-free survival; see legend to Table 8.


509

Table 11 Exceptionally Long-term Surivors Among Patients Treated with ATV-NDV Vaccine from Autologous Cell Cultures Median survival time expected

Median survival observed*

Ovarian carcinoma

⬃ 12 months

Glioblastoma multi-forme

⬃ 12 months

Pancreatic carcinoma

⬃ 12 months

Stomach carcinoma

⬃ 12 months

30 months DFS in 15/24 (73%) ⬎ 36 months in 3/25 (12%) ⬎ 36 months in 5/9 (55%) ⬎ 36 months in 3/7 (42%)

Tumor type

Reference

56 61 8 8

* Number of long-term survivors per number of patients vaccinated is indicated for the respective time period.

tumor cell cultures, we observed exceptionally long-term survivors [8,56,60]. Table 11 shows the median survival time that was expected from standard treatment and the median survival observed. It can be seen that a significant fraction of treated patients, varying from 12% to 73%, consisted of exceptionally long-term survivors. In a few long-term survivor patients, we recently succeeded in demonstrating, in peripheral blood, the presence of antitumor immune memory T cell reactivity [61]. This was observed even several years after the last vaccination, a finding consistent with a conditioning effect, as suggested earlier. Conclusions from Survival Data We like to critically review the obtained results and ask three relevant questions [60] that should be addressed to any cancer therapy: 1. Has the therapy the potential to cause antitumor effects? This question can be clearly answered positively. We were able to demonstrate in various tumor models as well as in studies with human cells that the vaccine can increase the activation of a variety of antitumor killer cells, including NK cells, macrophages [40,41], and cytotoxic T lymphocytes [63–65].

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Schirrmacher

The HN molecule of the virus was proven to play an important role in the activation of killer activity by induction of a strong IFN-␣ response[13,15,16], by upregulation of TRAIL on monocytes [41] and T cells [13], and by increasing costimulatory signals in CTL precursors [12] and T helper cells [32]. 2. Has this therapy a promising antitumoral activity in patients? Because most of our vaccination studies were performed in the postoperative adjuvant situation without residual tumor mass, no direct tumor responses could be determined. In these studies, an antitumor activity can only be deduced from the survival data. There were, however, singular cases of tumor responses in some studies. From 40 evaluable renal carcinoma patients treated with ATV-NDV and systemic IFN-␣, 5 exhibited a complete response (CR); 6, partial remission (PR); and 12, stable disease (SD, median 25 months). Twenty-three of forty (57.5 %) patients (CR, PR, and SD) appeared to have a significant survival advantage compared with patients with progressive disease during the treatment period and with a historic reference group [49]. In two glioblastoma-patients [61] with residual disease after operation, we saw several months after vaccination with ATV-NDV, complete remissions of the residual tumor masses. In addition, a subgroup of seven glioblastoma patients with residual tumor mass showed, after vaccination with ATV-NDV, a median survival twice that of a nonvaccinated comparable group [61]. The second question therefore can also be answered positively. 3. Does this therapy improve survival of treated patients in comparison to standard treatment or to nontreated patients, and what is the effect on quality of life? Because the side effects of this treatment are negligible, we conclude that the quality of life of treated patients is not affected in a negative way. The evidence level for survival benefit reached so far is that of Phase II studies. In some studies, we used pair-matched con-


511

trols from patients treated at the same clinic during the same time period without vaccination; in others we used historic controls; and in several studies we used actual internal controls with a different formulation of the same vaccine. Prospective randomized controlled studies are needed to validate the findings from the Phase II studies. The observed improvements in survival rates, between 20% and 36%, the observed median survival prolongation by about 100%, together with significant fractions of exceptionally long-term survivors, however, speak in favor of clinical efficacy of this type of therapy. A CRITICAL EVALUATION OF STANDARD THERAPIES Detrimental Effects of Chemotherapy on Memory T Cells Several of our Phase II clinical studies in which we introduced antitumor vaccination had to be combined with standard therapy such as chemotherapy (CT), radiotherapy (RT), or hormone therapy (HT) in the case of breast cancer. We therefore had to find out how to optimally combine immunotherapy with the other treatment procedures. Because CT and RT are known to be immunosuppressive, we tested the effect of these treatments on vaccination-induced DTH responses against autologous tumor cells in breast cancer patients. The results are shown in Table 12. When CT or RT was administered during the course of six vaccinations, there was a clear-cut detrimental effect on antitumor DTH responsiveness [42]. In contrast to the vaccinated control group (I), in which 46% showed significant increase, in the CT or RT group (II), only 8% showed significant increases and another 8% showed significant decreases of DTH reactivity. When testing previous antitumor DTH-responder patients under CT or RT therapy, only 20% responded to challenge by significant increases. Another 10% showed significant decreases. Fifty percent of such patients (II) showed decreased responses.

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Schirrmacher

Table 12 Effect of Chemotherapy or Radiotherapy on DTH Responsiveness in Breast Cancer Patients % of patients* I No CT or RT n ⫽ 67 Increase (⬎ 2 ⫻) Increase (⬍ 2 ⫻) No change Decrease (⬎ 2 ⫻) Decrease (⬍ 2 ⫻)†

46 22 21 4 3

II CT or RT during vaccination n⫽8 n⫽20** 8 40 16 8 28

20 20 20 10 50

III CT or RT 6 m before vaccination n ⫽ 15 33 14 7 – 47

IV CT or RT ⬎ 6 m before vaccination n⫽9 55 23 22 – –

CT ⫽ chemotherapy; RT ⫽ radiotherapy; DTH ⫽ delayed-type hypersensitivity; n ⫽ number of patients; m ⫽ months; aus. (From Ref. 44,54.) * Adjuvant CT or RT was either not given (group I), or given during vaccination (between the third and fourth of six vaccinations, group II), or 6 months before the vaccinations (group III), or more than 6 months before the vaccinations (group IV). ** Previous DTH responder patients. † Notice the increase in percent of patients in group II and III who, after vaccination and chemo- or radiotherapy, show a decrease of DTH reactivity.

When CT or RT was performed in a period of maximally 6 months before vaccination (group III), still 47% showed decreased responsiveness. In contrast, when vaccination was performed after a time period greater than 6 months (group IV) after CT or RT, a recovery of the original DTH responsiveness was noticed [42,54]. Based on these findings, we decided in all Phase II clinical studies in which chemotherapy or radiotherapy was involved to have a minimal distance of 6 months between these treatments and vaccination. In a separate study, we investigated the effect of adjuvant therapy in breast cancer on the content of memory T cells in bone marrow. Thirty-four patients who received adjuvant CT or HT were tested 24 months after primary therapy and compared with a group of primary operated patients who had not yet received these treatments and with a group of normal healthy donors. The results revealed that the proportion of T cells was significantly lower after adjuvant systemic therapy


513

than in the other two groups. Adjuvant therapy apparently had a significant detrimental effect not only on total T cell number but also on the content of memory T cells [66]. There were also significant differences between the CT and HT groups with respect to CD4 and CD8 T cells [66]. In contrast to chemotherapy, which preferentially affected CD4 T cells, tamoxifen treatment mainly affected CD8 T cells. The mechanisms behind these effects remain to be elucidated. The findings suggest that the two standard therapies in breast cancer, CT and HT, might have long-term detrimental effects on the immune system and affect negatively the memory content in bone marrow. A Need for Rational Re-evaluation of Standard Therapies that Cannot Provide Evidence for Survival Benefit The results from our clinical studies suggest that the immune system—and, in particular, antitumor immune memory T cells—can play an important role in long-term survival of treated cancer patients. Because many present-day adjuvant standard treatments such as CT, RT, and even HT are apparently immunosuppressive, the question arises whether these treatments nevertheless have a positive effect on long-term survival. An analysis of clinical trials performed with such treatment modalities reveals that a great majority of randomized trials shows only very little or no significant difference in overall survival between groups of patients treated by different protocols [67–69]. In spite of innovative techniques in tumor destructive therapies such as surgery, chemo- and radiotherapy, and some advances in the treatment of certain tumor types, overall cancer mortality in the United States could not be decreased in the past 20 years [67]. On the contrary, there was an age-corrected increase by about 6% [67]. With regard to chemotherapy of advanced carcinoma, independent meta-analyses revealed hardly any evidence for relevant improvements of overall survival [68,69]. For instance, a systematic review of published randomized trials involving 31,510 women with metastatic breast cancer who received

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cytotoxic and hormonal treatment revealed no evidence for survival improvement [70]. A systematic review and metaanalysis of individual patient data from 12 randomized trials of adult high-grade glioblastoma revealed very little benefit of chemotherapy [71]. Clinicians are often satisfied when a drug elicits a ‘‘tumor response’’ or relieves clinical symptoms even if there is no effect on overall survival. The assumption that a ‘‘tumor response’’ is linked with a survival benefit has been criticized as a ‘‘grand illusion’’ [68]. Because clinical therapy trials are very expensive, this field is strongly dominated by the pharmaceutical industry and therefore is profit oriented. Companies select trends and topics and also clinics and cooperation partners. Questions that are not product-related often are not financially supported. It does not come as a surprise that negative effects of drug treatments are rarely reported. Genentech Inc. alone reported in 2000, income of $750 million from the sale of its anti-cancer drugs. Companies selling so-called CAM can also make a good profit because patients long for such drugs.They also should provide evidence of effectiveness. In recent years, the protocols for good manufactural procedures (GMP) and good clinical practise (GCP) have become more stringent. It is generally accepted that only evidencebased medicine should be paid for by society’s funds. Because of these requirements for GMP and GCP and because Phase III clinical trials are very expensive, it is difficult for new biological treatment procedures to enter the market. On the other hand, one realizes that standard therapies that were introduced long ago, before these stringent requirements were established, are not being re-evaluated. It is argued that it would be unethical to compare a treated verum group with a nontreated control. One should oppose, however, that the small benefits reported from old studies that did not fulfill modern standards may not be acceptable anymore. A re-evaluation of survival benefits of adjuvant systemic therapies in comparison to relevant and proper controls is therefore warranted. A re-evaluation is also necessary because one cannot a priori exclude that a certain therapy could even have a nega-


515

tive effect on survival. A hopefully educational example is provided by postoperative radiotherapy of non–small-cell lung cancer. Although this treatment can improve a surrogate parameter—the time interval to local progression—the overall survival of such treated patients is reduced [72]. Radiotherapy can cause severe side effects such as pneumonitis and cannot prevent the development of distant metastases, which are likely more important with regard to overall survival than local recurrencies. Economic Evaluations Evaluations of treatments should include costs and consequences, namely health effects of the interventions. In cancer treatments, important health effects are disease-free survival, overall survival, toxicity, and the quality of life of the patients. Breast cancer is a major public health problem and therefore leads to considerable costs. Costs for antitumor vaccination by ATV-NDV are less than $10,000 per patient. In comparison, the health care costs of standard breast cancer treatment in the United States were estimated to be much higher. For instance, the incremental costs per life year gained were calculated to be $100,000 in a comparison of high-dose vs. standard chemotherapy and $300,000 in a comparison of chemotherapy plus tamoxifen for 5 years vs. 2 years [73]. The total health care costs of breast cancer in the Netherlands were estimated at 253 million Dutch guilders in 1988. This was about 13 % of the total health care costs of cancer. The highest costs were found for lymph node-negative and estrogen receptor-negative breast cancer patients, a fact which is linked with the low effectiveness of the treatment [73]. The Institute of Medicine of the U.S. Academy of Sciences provides further information on prospective randomized controlled studies and on routine patient care costs [74]. In recent years, companies have developed additional drugs that should alleviate side effects from the cytostatic drugs. This increases further the total health care costs without improving survival. In conclusion, treatments of cancer as a chronic disease are very expensive and a big burden to the public health

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budget. A re-evaluation of the effectiveness, based on survival data, may help to reduce the costs.

GENERAL CONCLUSIONS As an independent research scientist with more than 30 years of experience in tumor immunology and with great interest in the improvement of cancer therapy, I am used to the interpretation of data from experiments and from clinical trials. I therefore like to make some general conclusions from the situation as it appears to me at present: 1. There is a consensus that evidence-based medicine has to be the rule for any cancer treatment. Improvement of OS should always be the primary goal. This should therefore also be of importance for financial support through our health insurance systems. 2. In nine independent Phase II clinical studies, we observed considerable and significant improvements in OS when employing an immunotherapy protocol with a high-quality cancer vaccine. These studies were performed by different clinical partners at different clinics. The control groups used for comparison were either historic, pair-matched, or internal controls. Furthermore, the Phase II clinical studies were performed on different tumor types, including the most aggressive ones, such as pancreatic carcinoma and glioblastoma. They also included advanced metastasized stages of disease. Had I performed nine different animal experiments with nine different tumor lines and obtained each time significant survival improvements, I would be prepared to conclude that the treatment results are reproducible and that the treatment is broadly applicable. 3. The general health insurance systems in Germany are presently not prepared to pay for such treatments. 4. A comparison with the data basis for survival of the same types of cancer treated by conventional therapy


517

reveals lower survival rates. If one acknowledges this fact, the question arises as to why this may be. 5. In the following, I try to offer an explanation. The situation may have to do with the different effects that the respective treatments have on the patients immune system: While immunotherapies, performed with an optimized tumor vaccine, are boosting the patient’s immune system, in particular their antitumor immune memory T cell responses, conventional systemic standard therapies have detrimental effects on the immune system, including its memory part. Although the immunosuppressive and other side effects of such treatments are known for many years, no serious efforts have been undertaken by pharmaceutical companies or by clinicians to care about reconstituting the immune system after such treatments and of activating it specifically against the tumor by antitumor vaccination. Time for a Change! I believe that it is time for a change of paradigm in oncology. Dogma has been prevalent in oncology for a long time. Prominent surgeons dominated for decades the scenery with a theory that cancer can be treated like a localized disease if only the operation procedure is radical enough. Radical mastectomy, introduced by Halsted [75], was the treatment of choice for breast cancer of any size or type, regardless of the patient’s age, for 80 years. Recent randomized studies now reveal that less extensive breast-conserving surgery can achieve similar 20-year survival rates [76,77]. Although the rate of local recurrence was higher in the group that received breast-conserving therapy, the overall survival rate was the same in both groups. The prognosis of breast cancer therefore depends less on the extent of local surgery than on the presence or absence of occult distant foci of metastatic cells and their control. As a result of these trials, about 300,000 women with early breast cancer worldwide each year can now undergo breast-conserving surgery rather than radical mastectomy.

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Schirrmacher

Hopefully, in the future, a similar development will lead to a better application of chemotherapy, avoiding overdosing and avoiding application in patients who do not profit from it. Sensitive in vitro assays allowing pretesting of the chemosensitivity of a tumor [78] may help to more effectively apply chemotherapy to cancer patients. Conservative treatment modalities such as surgery, chemotherapy, or radiotherapy should be evaluated in the same way as all new treatment modalities, namely, on the basis of evidence for survival benefit in randomized controlled studies. Claims for financial support should be subject to the same critical evaluation procedures. The survival benefit from any cancer treatment must become absolute priority. All other surrogate parameters are secondary. Let us now go back to the drawing board for an evaluation of the effect of different strategies for cancer treatment on immune memory and long-term survival. Change of Paradigm I am proposing that in many situations, in which tumor cells have already disseminated in the body at the time of operation, it is very difficult for any type of additional therapy to eradicate the last disseminated tumor cell in the body. I am convinced that this is not necessary because the host’s immune system is basically capable of controlling and preventing outgrowth of tumors from such disseminated cells as long as the tumor burden is low and below a clinically detectable level. Such an immune control of residual tumor burden, however, requires an intact immune system and, in particular, a certain threshold of antitumor immune memory T cells. It has been our experience that the existence of such immune memory can be the basis for a very efficient antitumor immune control being capable of resisting tumor challenge by a lethal tumor dose. It is of great importance to study the many factors that are important for the maintenance of long-term immune memory because this is very relevant for long-term survival. Therefore, the tumor- bearing host and, in particular, the patient’s immune system should play an active part and be integrated in any cancer therapy strategy.


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The Tumor-Bearing Host Contributes with Immune Memory a Component of Importance for Survival Figures 4 through 6 are designed to illustrate what is meant by this proposition. Antigen-specific T cell-mediated immune responses are characterized by a first expansion phase, a second retraction phase, and a third memory phase. Figure 4 illustrates these three phases for a primary immune response (left) and a secondary immune response (right). Secondary immune T cell responses are initiated by antigen-experienced memory T cells and are faster and superior to primary T cell

Figure 4 The three phases of immune T cell responses. (A) primary T cell responses are initiated by naı¨ve antigen-specific T cells [the frequency of which is usually very low (⬍ 1 in 100,000 T cells)] upon interaction with antigen-presenting dendritic cells in secondary lymphoid organs. (B) Secondary T cell responses are initiated by antigen-experienced memory T cells. These responses are faster than those of naı¨ve T cells and have less stringent activation requirements. They can be stimulated by high-quality tumor cell vaccines. Primary and secondary immune responses can be each divided into three phases (a–c): (a1,2) expansion phase; (b1,2): retraction phase; (c1,2): memory phase

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Figure 5 Principle effects of immunotherapy (D, F) or chemotherapy (B,C,E,G) on immune memory in different situations. A level of pre-existing immune memory in cancer patient before any therapy B detrimental effect of neo-adjuvant chemotherapy on pre-existing memory C detrimental effect of adjuvant chemotherapy on pre-existing memory D positive effect of postoperative vaccination: increase of memory to relevant threshold E detrimental effect of adjuvant chemotherapy during vaccination on maintenance of long- term memory F positive effect of booster vaccination if performed more than 6 months after chemotherapy; increase of memory to relevant threshold G unsuccessful effect of booster vaccination if performed less than 6 months after chemotherapy; memory decreases below relevant threshold

responses initiated by naı¨ve T cells. Also, the activation requirements for immune memory T cell responses are less stringent than those for naı¨ve T cells (also discussed in ‘‘Characteristics of Memory T Cells,’’ in the third section, ‘‘Development of the New Concept in Animal Tumor Models,’’ above). Thus, tumor vaccines can be specifically designed to stimulate memory T cell responses and we believe that this is the case with the tumor vaccine ATV-NDV.


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Figure 6 Different effects of therapeutic interventions for cancer treatment. A Tumor progression (if untreated or if therapy is ineffective) B complete cure (usually after surgery, when tumor has not spread) C, E, G stable disease; clinically tumor free; residual tumor cells under control of immune memory D, F, H tumor recurrence after 1⬚, 2⬚ or 3⬚ intervention

Figure 5 illustrates the effects of immunotherapy or chemotherapy on immune memory in different situations of cancer patients. The situations illustrate what we have examined in a variety of clinical situations and summarized in this review. Figure 6 illustrates, in general, different effects of therapeutic interventions for cancer treatment. Until a tumor becomes clinically detectable, a transformed somatic cell must have undergone approximately 30 cell divisions to reach a tumor cell number of approximately 109, making up a tumor mass of about 1 g. If the tumor would be dividing further for 10 more cell divisions (situation A) it would reach the maximal tolerable tumor load of 1012 cells, representing a mass of about 1 kg. Clinical therapeutic intervention by surgery usually starts at a tumor size of 1 g to 10 g. If, at the time of surgery, the tumor has not disseminated, a complete cure by surgery can be achieved (situation B). If therapeutic intervention by

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surgery or any other means achieves a tumor reduction above 99%, there may still be millions of tumor cells left in the body that cannot be reached by these interventions. C illustrates a situation that is stable because immune memory is able to control a remaining tumor load after therapy. Such active immune control could cause long-term survival, as long as a certain memory threshold remains and the tumor is not developing immune escape variants. Situation D illustrates an effect where a tumor response to primary treatment may be greater 90%. Nevertheless, following some time delay, the tumor will grow again and kill the patient unless there is a second therapeutic intervention. E illustrates a situation in which a secondary intervention could reduce the remaining tumor load below the memory threshold so that the cells could become subject to immune control. H and F show situations in which the tumor eventually has become resistant to the type of treatments. G shows a situation in which a third therapeutic intervention could reduce the tumor load below a detectable level. Figure 6 is shown basically to demonstrate the new concept that therapeutic interventions might be sufficient if they reduce the tumor burden below a certain threshold. This can often be further controlled by the immune system provided that it is not damaged by either the tumor or by the intervention itself. Situations C and E illustrate an important change of paradigm. In these situations, the tumor is controlled by a combination of therapeutic intervention and by the patient’s own immune system. This could result in a long-term clinically stable situation. In support of this new concept, McCoy et al [79] recently demonstrated that cell-mediated immunity to TAA is a better predictor of survival than stage, grade, and lymph node status in early stage breast cancer. ACKNOWLEDGMENT Our concepts and procedures of preparation of individual vaccines are admittedly unusual but a conflict of interest cannot


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be claimed. None of the clinical studies presented has been supported by a pharmaceutical company nor by a public grant. The patents I hold on the ATV-NDV technology (EP 03331 102, US 5273745), on NDV HN DNA and protein (EP/0689596), and on NDV-binding bispecific antibodies (US 5911987; 4407 538) remain unused for many years. We are particularly grateful for private support from the Mhlschlegel Stiftung and the Dietmar Hopp Stiftung. I would like to thank the following clinicians for their engagement and motivation, without whom none of these studies would have been possible. Their names will be associated with the respective cancer type: Colorectal (primary advanced): D. Ockert, N. Beck, E. Stoelben, J. Flechtenmacher, E. Hagmller, M. Nagel, H.-D. Saeger; Colorectal (liver metastasis): P. Schlag, W. Liebrich, B. Lehner, M. Manasterski; Renal carcinoma: S. Pomer, R. Thiele, D. Brkovic, G. Staehler; Ovarian carcinoma: V. Mo¨bus, S. Horn, M. Sto¨ck; Breast carcinoma: T. Ahlert (http:// www.biotech-praxislab.de/), G. Bastert, W. Sauerbrei, S. Ruhland, B. Bartik, N. Simiantonaki, J. Schumacher, B. Hcker, M. Schumacher, I. J. Diel, E.F. Solomayer; Metastatic melanoma: T. Pro¨bstle, Kamanabrou; Glioblastoma: C. HeroldMende, H. H. Steiner; Pancreatic and gastric carcinoma: R. Gerhards. For excellent contributions and help in this translational research I would like to thank the following scientists from my group: V. Umansky, P. Beckhove, M. Feuerer, and P. Fournier. REFERENCES 1. Gallucci S, Matzinger P. Danger signals: SOS to the immune system. Curr Opin Immunol 2001; 13:114–119. 2. Akira S, Takeda K, Kaisho T. Toll-like receptors: critical proteins linking innate and acquired immunity. Nat Immunol 2001; 2:675–680. 3. Luster AD. The role of chemokines in linking innate and adaptive immunity. Curr Opin Immunol 2002; 14:129–135. 4. Heicappell R, Schirrmacher V, von Hoegen P, Ahlen T, Applehans. Prevention of metastatic spread by postoperative im-

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24. Schirrmacher V. T-cell immunity in the induction and maintenance of a tumor dormant state. Semin Cancer Biol 2001; 11: 285–295. 25. Veiga-Fernandes WU, Bourgeois C, McLean A, Rocha B. Response of naive and memory CD8Ⳮ T cells to antigen stimulation in vivo. Nat Immun 2000; 1:47–53. 26. Kaech SM, Wherry EJ, Ahmed R. Effector and memory T cell differentiation: implications for vaccine development. Nature Rev 2002; 2:251–262. 27. Mahnke Y, Schirrmacher V. A novel tumor model system for the study of long-term protective immunity and immune T cell memory. Cell Immunol 2003; Feb 221(2):89–99. 28. Karrison TG, Ferguson DJ, Meier P. Dormancy of mammary carcinoma after mastectomy. J Natl Cancer Inst 1999; 91: 80–85. 29. Pantel K, Otte M. Occult micrometastasis: enrichment, identification and characterization of single disseminated tumor cells. Cancer Biol 2001; 11:327–337. 30. Feuerer M, Rocha M, Bai L, Umansky V, Solomayer EF, Bastert G, Diel IJ, Schirrmacher V. Enrichment of memory T cells and other profound immunological changes in the bone marrow from untreated breast cancer patients Int J Cancer 2001; 92([4]):1–1. 31. Feuerer M, Beckhove P, Bai L, Solomayer EF, Bastert G, Diel IJ, Heep J, Oberniedermayr M, Schirrmacher V, Umansky V. Therapy of human tumors in NOD/SCID mice with patient derived re-activated memory T cells from bone marrow. Nat Med 2001; 7([4]):452–458. 32. Termeer CC, Schirrmacher V, Bro¨cker EB, Becker JC. Newcastle-Disease-Virus infection induces a B7-1/ B7-2 independent T-cell-costimulatory activity in human melanoma cells. Cancer Gene Ther 2000; 7([2]):316–323. 33. Ghanta VK, Hiramoto NS, Soong SJ, Hiramoto RN. Conditioning of the secondary cytotoxic T-lymphocyte response to YC8 tumor. Pharmacol Biochem Behav 1995; 50([3]):399–403. 34. Exton MS, von Auer AK, Buske-Kirschbaum A, Stockhorst U, Gobl U, Schedlowski M. Pavlovian conditioning of immune


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44. Ahlert T, Bastert G, Schirrmacher V. Mamma- und Ovarialkarzinom mit autologen virusmodifizierten Tumorzellen, aktivspezifische Immuntherapie (ASI). Theorie, Praxis Perspektiven. T. W. Gyna¨kologie 1989; 2:359–367. 45. Lehner B, Schlag P, Liebrich W, Schirrmacher V. Postoperative active specific immunization in curatively resected colorectal cancer patients with virus-modified autologous tumor cell vaccine. Cancer Immunol Immunther 1990; 32:173–178. 46. Manasterski M, Liebrich W, Mo¨ller P, Schirrmacher V, Schlag P. Active specific immunotherapy in colorectal cancer and melanoma. In: Klapdor R, Ed. Recent Results in Tumor Diagnosis and Therapy. Zuckschwerdt Verlag: Mu¨nchen:, 1990:499–504. 47. Lehner B, Liebrich W, Mechtersheimer G, Schirrmacher V, Schlag P. Charakterisierung und erste Ergebnisse einer aktiven spezifischen Immuntherapie bei Patienten mit colorectalem Carcinom. Langenbeck’s Arch. Chir (Suppl. Chir. Forum) 1989:513–517. 48. Schlag P, Manasterski M, Gerneth TH, Hohenberger P, Dueck M, Herfarth CH, Liebrich W. SchirrmacherV. Active specific Immunotherapy with NDV modified autologous tumor cells following liver metastases resection in colorectal cancer: first evaluation of clinical response of a Phase II trial. Cancer Immunol Immunother 1992; 35:325–330. 49. Pomer S, Thiele R, Staehler G, Lo¨hrke H, Schirrmacher V. Tumor vaccination in renal cell carcinoma with and without interleukin-2 (IL-2) as adjuvant. A clinical contribution to the development of effective active specific immunization. Urologe A 1995; 34:215–220. 50. Pomer S, Schirrmacher V, Thiele R, Lo¨hrke H, Staehler G. Tumor response and 4 year survival data of patients with advanced renal cell carcinoma treated with autologous tumor vaccine and subcutaneous r-IL-2 and IFN-Alpha 2b. Int J Oncol 1995; 6:947–954. 51. Bai L, Beckhove P, Feuerer M, Umansky V, Solomayer EF, Diel IJ, Schirrmacher V. Cognate interactions between memory T cells and tumor antigen presenting dendritic cells from bone marrow of breast cancer patients: bi-directional cell stimulation survival and anti-tumor activity in vivo. Int J Cancer 2003; 103: 73–83.


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61. Steiner HH, Bonsanto MM, Beckhove P, Brysch M, SchueleFreyer R, Geletneky K, Kremer P, Golamrheza R, Bauer H, Kunze S, Schirrmacher V, Herold-Mende C. Anti-tumor vaccination of patients with glioblastoma multiforme in a case-control study: feasibility safety and clinical benefit. J Clin Oncol, in press. 62. Schirrmacher V, Feuerer M, Beckhove P, Ahlert T, Umansky V. T cell memory, anergy and immunotherapy in breast cancer. J Mammary Gland Biol Neoplasia 2002; 7([2]):201–208. 63. Hoegen P, Weber E, Schirrmacher V. Modification of tumor cells by a low dose of Newcastle Disease Virus: augmentation of the tumor-specific T cell response in the absence of an antiviral response. Eur J Immunol 1988; 18:1159–1166. 64. Schild HJ, von Hoegen P, Schirrmacher V. Modification of tumor cells by a low dose of Newcastle Disease Virus: II. Augmented tumor specific T cell response as a result of CD4Ⳮ and CD8Ⳮ immune T cell cooperation. Cancer Immunol Immunother 1988; 28:22–28. 65. Von Hoegen P, Zawatzky R, Schirrmacher V. Modification of tumor cells by a low dose of Newcastle Disease Virus: III. Potentiation of tumor specific cytolytic T cell activity via induction of interferon, alfa, beta. Cell Immunol 1990; 126:80–90. 66. Solomayer EF, Feuerer M, Bai L, Umansky V, Meyberg GC, Bastert G, Schirrmacher V, Diel IJ. Influence of adjuvant hormone therapy and chemotherapy on the immune system analysed in the bone marrow of patients with breast cancer. Clin Cancer Res 2003; 9:174–180. 67. Beuth J, Ed Grundlagen der Komplementa¨r-Onkologie. Theorie und Praxis: Stuttgart: Hippokrates Verlag, 2002. 68. Moss RW. The grand illusion of chemotherapy. Deutsche Zeitschrift fu¨r Onkologie 2001; 33:15–18. 69. Abel U. Die zytostatische Chemotherapie fortgeschrittener Karzinome: 2. Aufl.. Stuttgart: Hippokrates-Verlag, 1955. 70. Fossati R, Confalonieri C, Torri V, Ghislandi E, Penna A, Pistotti V, Tinazzi A, Liberati A. Cytotoxic and hormonal treatment for metastatic breast cancer: a systematic review of published randomized trials involving 31 510 women. J Clin Oncol 1998; 16:3439–3460.


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5 Newcastle Disease Virus: Its Oncolytic Properties JOSEPH C. HORVATH St.Joseph’s Hospital Cancer Institute Biotherapy Research Laboratory, University of South Florida College of Medicine, Department of Medical Microbiology & Immunology Tampa, FL

INTRODUCTION Newcastle disease afflicts at least 236 species from 27 of the 50 orders of birds and is the most serious infectious disease problem in the poultry industry as well as backyard chicken farming worldwide [1]. The causative agent is Newcastle disease virus (NDV), a paramyxovirus. Highly pathogenic (velogenic) strains of NDV are responsible for epidemics, whereas moderate or avirulent (mesogenic and lentogenic) strains are 533

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frequently used as vaccines. The molecular characterization of pathogenic and less pathogenic strains is relatively easy and straightforward [2,3]. In spite of high contagiousness and severity of the disease in birds, NDV causes only very mild transient infection in humans, with no difference between pathogenic and less pathogenic strains [4–6]. Medical interest in NDV soared since it was discovered that the virus is oncolytic—i.e., it preferentially kills human tumor cells, while normal cells are spared [7–9]. THE VIRION Newcastle disease virus is a member of the Paramyxoviridae family; it is an enveloped virus with a nonsegmented (ⳮ) strand RNA genome of 15186 nucleotides (nt). The order of viral proteins encoded by the genome is nucleoprotein (NP)phosphoprotein (P)-matrix (M)- fusion (F)- hemagglutininneuraminidase (HN)- ‘‘large’’, RNA polymerase (L). The coding region is flanked by regulatory sequences named leader and tailer at the 3′ and 5′ ends. Further proteins are translated from the P protein gene by mRNA editing (vide infra). At the beginning and the end of each gene, there are transcriptional control sequences that are transcribed to the polycistronic mRNA. The core N as well as the P and L proteins are attached to the RNA genome and form the helical nucleocapside structure, which is the template for mRNA and antigenome synthesis. The HN and F proteins embedded in the viral envelope surrounding the nucleocapsid play a role in the attachment of the virus to and fusion with the cell membrane. The M protein fills the space between the nucleocapsid and the envelope. Until recently, NDV was listed as a member of the Rubulavirus genus; however, it was different enough from the rest of the members of that genus to form the Avulavirus genus [6]. THE VIRAL REPLICATION CYCLE The NDV replication cycle starts with binding of the virion to protein and lipid sialoglycoconjugate cell membrane receptors

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through HN and F proteins in concert. The hydrophobic fusion peptide domains of the F protein homotrimers are embedded in the cell membrane and induce its fusion with the virion and with other surrounding cells, causing syncytium formation (for review see Ref. 10–12). Following fusion, the helical viral nucleocapsid is released into the cytoplasm. Viral replication takes place in the cytoplasm. It is remarkable, however, that the M protein contains a dipartite nuclear localization signal and a large portion of it is transported to the nucleus and nucleolus [13–15]. The significance of the nuclear localization of the M protein is not known but besides being a structural viral component, M proteins of several paramyxoviruses also inhibit host-cell and (during packaging and budding) viral transcription [16,17]. The viral HN and F proteins are synthesized as precursors and further processing is required for their biological activity. A 90 aa (amino acid) peptide is removed from the C-terminal of HN (a type II membrane protein) by cellular enzymes [18]. The F protein (type I membrane protein) is also cleaved close to the N-terminal, distal to the extensively hydrophobic fusion peptide, resulting in two fragments (F1 and F2) held together by a –S–S– bridge. The enzyme(s) responsible for the cleavage is probably furin and/or PC6 [19]. Cleavage of Fo protein renders the virus infective as well as determines host specificity and pathogenicity (vide infra). The mRNA transcript from the P gene is either translated unmodified to the P protein or edited at the V ORF internal editing site by insertion of one or two G residues. The edited mRNA with the frameshifts enables the translation of the V and W proteins with an N-terminal identical to that of the P protein and different C-terminal amino acid sequences [20–22]. The primary transcripts and the antigenome (after translation and accumulation of viral proteins) are synthesized by the viral RNA polymerase, a complex of the P and L proteins using the viral RNA genome, covered and protected with the nucleoprotein (N), as template. The genomic RNA–nucleoprotein complex together with the RNA-dependent RNA polymerase (PⳭL) is encapsidated and migrates to the cell membrane, where it becomes associated with the matrix (M) protein and the viral envelope and leaves the cell by

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budding and detachment when the HN clips the sialoglycoconjugate cellular receptor (reviewed in Ref. 11). Production of host macromolecules is shut off by the late phase of the viral replication [23]. VIRULENCE, HOST SPECIFICITY Newcastle disease virus is an avian pathogen and seldom causes disease in mammals; conjunctivitis with preauricular lymph node involvement is a rare and self-resolving consequence of NDV exposure in humans. Sialylglucoconjugate receptors are quite ubiquitous on mammalian cells and shortage in receptor numbers does not seem to be the reason for cell specificity. Some viral precursor proteins need further processing to be functional and changes in the cleavage site influence processing efficiency. Virulent NDV strains with F0 protein having two or more basic amino acids at the cleavage site are processed by the ubiquitous endoproteases furin and PC6 in avian cells and multiple cycles of viral infection affect different organs [24]. F0 proteins of less pathogenic NDV strains contain only one basic amino acid residue and are not processed by the same enzyme. Cleavage does not happen in tissue culture; the produced virions remain noninfectious and only one viral cycle occurs. When avirulent NDV replicates in chicken embryos, factor Xa (the necessary enzyme for cleavage of F0 with one basic amino acid residue) is present in the allantois fluid and surrounding tissues of the embryonated eggs, assuring production of infectious virus particles. In animals, infection with such NDV is restricted to the respiratory and gastrointestinal tracts [25–28]. A recombinant F protein (noncleavable in nature) derived from the avirulent NDV Queensland strain has been expressed in mammalian cells and in vitro processed to mature form with trypsin treatment [29]. Subtilisinlike proprotein convertase enzymes furin, PACE4, PC6, etc. are able to process the F protein of virulent NDV strains in mammalian cells, but PACE4 shows low activity [19,30]. Changing the cleavage site of the F protein from GRQKR (lentigenic phenotype) to RRQKR (mesogenic phenotype) of the LaSota NDV


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strain increased its neurovirulence but not to the level of the mesogenic Beaudette strain. That clearly shows that the F protein is not the only viral factor that determines virulence [31]. Newcastle disease virus is a strong inducer of interferon (IFN) in mammalian cells, but no IFN response is observed in the natural host. The viral V protein is responsible for shutting off IFN synthesis in avian cells; it has no effect on mammalian cell IFN production [32–34]. Recombinant NDV with a mutated P gene mRNA editing site or a truncated V protein (of which the C-terminal was deleted) shows a heavily compromised replication in chicken embryo fibroblasts, whereas it grows well in IFNⳮ VERO cells [35]. Interferon induction is not restricted to the dsRNA because the viral proteins HN, M, and the uncleaved F precursor are also IFN inducers [36]. NEWCASTLE DISEASE VIRUS AS AN ONCOLYTIC AGENT Spontaneous tumor regression observed after different naturally occurring virus infections or vaccination with attenuated lyssa virus of a tumor-bearing person suggested that certain viruses replicate in and kill human tumors (37, also Sinkovics in this volume). Newcastle disease virus emerged early as an oncolytic agent when it was discovered that the virus was able to kill established Ehrlich ascites and other tumors while sparing normal tissues[8,38,39]. The reason for this tumor-cell specificity is not clear. Clinical trials with several NDV strains as direct oncolytic agents are published (vide infra); our clinical experience is with the 73-T strain developed by W. Cassel. The best-characterized and most-often-used oncolytic NDV 73-T strain was developed and described by W. Cassel (retired, Emory University, Atlanta, GA) from a field isolate of R. Love [8]. The 73-T virus is neurovirulent, killing 1-day-old chicks by paralysis after intracerebral inoculation; after intramuscular inoculation, viral replication occurs in the infected animals but no clinical disease is observed. Nucleotide

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sequence analysis fragments of the F gene representing the cleavage site, amplified by Reverse Transcription-Polymerase Chain Reaction (RT-PCR), revealed similarity of 73-T to pathogenic strains (J.C. Horvath, unpublished). See comparison of the cleavage site (printed bold) and flanking amino acid sequence of the 73-T strain compared to the consensus sequence between amino acid 97 and amino acid 146 of the F protein, published by D. King and B. Seal. [3]. The two basic amino acids characteristic of the velogenic strains are labeled with *. (This work has been supported, in part, by the Molecular Biology Core Facility at the H. Lee Moffitt Cancer Center & Research Institute, Tampa, FL.) Consensus 97 ESIPRIQGSA TTSGRRQKR FVGAIIGSVA LGVATAAQIT AAAALIQANQ 146 ::::::: : 73–T

:::::::::: : ::::: :: :::::::::: :::::::: :

ESIPRIQESV TTSGGRRQKR FIGAIIGGVA LGVATAAQIT AAAALIQAKQ

Treatment of Ehrlich ascites tumor-bearing mice with 73-T was curative up to 6-day-old tumors and no ascites developed during a 2-month observation period thereafter. The life of mice with tumors older than 6 days when receiving 73-T treatment was prolonged compared with untreated tumor-bearing controls. The first application of 73-T as an oncolytic agent was done by W. Cassel in a woman with a previously untreated, inoperable cervix carcinoma; a single intratumoral NDV injection resulted in extensive sloughing of tumor tissue and regression of lymph node metastases, with considerable subjective improvement; however, the patient expired 7 months later [8]. Genetically immunosuppressed SCID (Severe Combined Immunodeficiency) mice carrying xenografted human neuroblastoma or fibrosarcoma responded well to a single intratumoral injection of NDV 73-T and showed complete or partial remissions [40–42]. The oncolytic property of 73-T was confirmed after intratumoral inoculation into different human cancer xenografts and was observed with systemic application of the virus as well [43]. Sensitivity of lymphoma cells to NDV oncolysis exceeds that of lymphoblastoid cell lines. Resting lymphocytes are nonpermissive to NDV infection. Lymphocytes stimulated with phytohemagglutinin, however, moderately support virus replication (44; J. C. Horvath’s own observations).


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Newcastle disease virus induces extensive apoptosis (A) and necrosis in infected chicken lymphocytes within 3 hours after infection. The cause of death in infected chicken embryos is A in the brain, heart, thymus, and other organs [45,46]. Newcastle disease virus induces lytic infection in human tumor cell lines, whereas normal fibroblasts are resistant to viral infection. Although the exact mechanism of selective killing of tumor cells is not known, direct effects of the virus on the tumor cells and A are involved. Newcastle disease virus causes A in PC12 rat phaeochromocytoma cells [47,48]. The way NDV induces A is not certain; the authors conclude that major mitogen-activated protein kinase pathways (including the stress-inducible c-Jun N-terminal kinase pathway and p38 pathway) or mechanisms regulated by reactive oxygen species do not appear to have a role in virus-induced cell death. Cell burst occurs when progeny viruses leave the host cell. The viral replication cycle in natural host chicken embryo fibroblasts is about 6 hours. Some cells start to leak macromolecules 2 hours after NDV infection [49]. Melanoma cells infected with NDV 73-T show intensive syncytium formation and ballooning degeneration, followed by the appearance of apoptotic bodies and infectious virus in the cell-free medium within a 24-hour replication cycle. In a syngeneic system of transplantable animal tumors, virus-induced innate and adaptive immune mechanisms (NK cells and macrophages, antibody or cell-mediated immune response, cytokine production, etc.) are responsible for oncolysis as well [50]. MECHANISM OF ACTION OF ONCOLYTIC NEWCASTLE DISEASE VIRUS Interaction of Viral and Host Proteins and Interference with the Cell Cycle The V protein of Simian virus 5 (member of the Rubulavirus genus, closely resembling NDV) interacts with and inactivates the damage-specific DNA binding protein (DDB), a host protein involved in recognition of damaged DNA for nucleotide

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excision repair [51–53]. In uninfected cells with no DNA damage, DDB interacts with the transcription factor E2F1 and overrides its inhibition by Rb, allowing the cell to cycle [54]. When DDB binds to damaged DNA, the E2F1-Rb complex is unchallenged and the cell cycle slows down during DNA repair. The advantage to slowing down the cell cycle during viral replication is not clear, but viral macromolecule synthesis is probably more efficient when the host cell is not in division [55]. The Interferon Pathway Definitions Interferon is part of the innate immune system and is considered to be a tumor suppressor gene; it has cell-cycle regulatory, antiproliferative, and anti-angiogenic effects. Interferons regulate the expression of pro-apoptotic and anti-apoptotic genes and the IFN pathway leads to apoptosis. Interferons are secreted by virus-infected cells and act upon surrounding and distant cells. Viral HN by itself (without viral replication) triggers the production of IFN␣ and the tumor necrosis factor (TNF)␣-related apoptosis-inducing ligand (TRAIL) by mononuclear cells [56]. Interferon-␥ induction by NDV in peripheral blood mononuclear cells (PBMC) is weak and IFN␥ production by PBMC of cancer patients is diminished compared with healthy controls [57,58]. For that reason, our discussion is focused on type I IFNs. Interleukin (IL)-2 treatment, however, increases IFN␥ secretion by activated PBMC [59] and should be tried in combination with virotherapy. Interferon-␣ and IFN␤ exercise their antiviral, antiproliferative, and immunomodulatory actions by binding to IFN receptors IFNAR1 and IFNAR2, transmembrane proteins associated with protein tyrosine kinases Jak1 and Tyk2. The activated kinases then phosphorylate the tyrosine residue Tyr466 on IFNAR1 and the activated receptor–kinase complex attracts the signal transducer and activator of transcription 2 (STAT2). Phosphorylated STAT2 (Tyr690) forms homo- and heterodimers with STAT1 and interferon regulatory factor


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(IRF)-9 to form the IFN-stimulated gene factor 3 (ISGF3). Interferon-␣–activated factor (homodimer of phosphorylated STAT1) and IGSF3 are transported to the nucleus, associated with other IRFs, and bind to consensus DNA motives TTNCNNNAA found in the promoter region of IFN-regulated protein genes (IFN-stimulated genes; ISGs) to activate their transcription, including IFN␣ itself (for a review see Ref. 11). Pro-apoptotic Genes Regulated by Interferons Interferon-␤ induces A in melanoma, ovarian carcinoma, and multiple myeloma cell lines in vitro and in xenotransplanted tumors (see review in Ref. 61). Interferon-␥ suppresses the growth of both platinum-sensitive and resistant ovarian carcinoma cell lines [62]. Whereas short (20 hours) exposure to IFN␥ was not associated with antiproliferative effect in ovarian carcinoma cells and xenotransplanted tumors in mice, continuous exposure over several days resulted in growth suppression and A [63]. Apoptosis induced by IFN␥ is mediated by IRF-1 [64]. Encouraging results in small clinical trials warrant further evaluation of the therapeutic value of IFN␥ in ovarian carcinoma. In general, IFNs induce the expression of numerous A-related proteins. Apoptosis plays a major role in the antitumor effect of IFN; it is executed independently of p53, making cells with mutated p53 sensitive to IFN-induced A as well. Apoptosis induced by IFNs does not correlate with the cellular level of Bax and Bcl-2 either [65]. Oligonucleotide microarray analysis of IFN-treated tumor cells revealed a set of genes playing a role in A and helped render understanding of the role of IFNs in A [61]. The role of Fas/APO-1/CD95 and its ligand (FasL) in physiological A is well known: [1] peripheral deletion of activated T cells in absence of antigens (but keeping memory T cells intact); [2] elimination of virus-infected or tumor cells; and [3] guarding immunologically privileged sites (testicles, eye, etc.). Expression of Fas is upregulated upon IFN␣ treatment in hematological malignancies [66,67]. Tumor necrosis factor-related apoptosis-inducing ligand is also induced by IFNs in a tissue or tumorspecific manner. Interferon-␤ is a better inducer of TRAIL (and

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A) in melanoma and ovarian carcinoma, whereas multiple myeloma responds better with upregulated TRAIL to IFN␣2 [68]. X-linked inhibitor of apoptosis (XIAP)- associated factor-1 (XAP-1) is also an IFN-induced pro-apoptotic and tumor suppressor gene. ). X-linked inhibitor of apoptosis-associated factor-1 neutralizes the inhibition of caspases by XIAP and they co-localize from the cytoplasm to the nucleus. Overexpression of XAP-1 sensitizes the tumor cells to TRAIL-mediated A [69]. Expression of XAP-1 is suppressed in various cancers by promoter hypermethylation [70]. Caspases (cysteine proteases), initiators and effector enzymes of A, are also induced by IFNs. Caspase-4 is induced by IFN␣ and IFN␤ in melanoma, human umbilical vein endothelial cells (mechanism of antiangiogenesis by IFN), and fibrosarcoma cell lines, whereas IFN␥ initiates expression of caspase-4 and 8 in breast cancer cell lines [71]. Other proapoptotic genes induced by IFNs include IRFs, double-stranded RNA-dependent protein kinase (PKR, vide infra), and 2-5A oligoadenylate synthetases. Oligoadenylate synthetases are activators of DNA and RNA-degrading endonucleases, acting through formation of 2’-5’–linked oligoadenylates from adenosine triphosphate (ATP). Further induced are RNase L (mutated in aggressive prostate carcinoma), galectin-9 (downregulated in melanoma), death-associated protein kinase (a tumor suppressor gene lost in 50% of human malignancies, such as bladder and renal cell carcinomas, B-cell lymphoma, breast cancer, and pituitary tumors) (for review see Ref. 61). Newcastle disease virus might kill tumor cells with an intact, functioning IFN system through A induction. Such infection would result in no progeny virus production in tumor cells and would explain why mega-dose treatment is needed to achieve clinical response (vide infra). Why are normal cells infected with NDV not victims of A? In search for an explanation as to how NDV preferentially kills tumor cells, we shall hypothesize that in the host, tumor cells escape surveillance of the innate immune system, partly because they are in a nonresponsive state to the antiproliferative action of IFN. The defensive activity has to include blockade both of endogenous IFN production and response to exoge-


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nous IFN. Tumor cells with such a nonfunctional IFN system would fall victim to NDV infection. Type I Interferon Receptors Tumor cells are continuously exposed to low amounts of IFN␣ and IFN␤ from surrounding stromal or virus-infected cells [60]. In IFNAR knockout mice, when inoculated with different types of syngeneic transplantable tumor cell lines, tumor development and mortality are increased compared with IFNARexpressing controls, showing that IFN is a natural mediator of innate immunity against tumor development [72]. Expression of IFNAR in neuroblastoma correlates with grade and appears to be a prognostic factor [73]. S. Navarro et al studied IFNAR-receptor expression in human fetal and adult tissues as well as in different tumors. All normal adult and fetal tissues and most, but not all, tumors (melanomas, adenocarcinomas of bladder, kidney, small intestine, lung, and breast) expressed the IFNAR; however, lymphomas, sarcomas, and endocrine tumors were found to be negative for type I IFNreceptor expression [74]. Exposure of tumor cells to IFN might turn down IFN-receptor expression, as observed with Daudi lymphoblastoid cell lines [75]. Expression of IFNAR is normal in renal cell carcinoma, even in metastatic disease [76]. Tumor Cell Interference with Interferon and the Interferon Signaling Pathway Interferon induction requires the formation of the ISGF3 complex, which then activates the IRF-7 gene encoding for a transcription factor, inducing the expression of IFN [77]. In a fibrosarcoma cell line, IFN␣ induction is shut down by hypermethylation of the IRF-7 gene promoter [78]. Our standing concept is that impaired IFN expression renders cancer cells vulnerable to NDV infection. The antiproliferative effect of IFN on melanoma cells is well documented, but several cell lines become resistant. Different pathways must exist that confer, to the cells, resistance to the growth-inhibitory effect of IFN [79–81]. Signal transducer and activator of transcription-1 is anti-oncogenic; its

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expression is often downregulated in tumor cells [82]. In uterine cervical cells infected with high-risk oncogenic human papillomavirus serotypes, IFN production is diminished or shut off [83]. Melanoma cell lines with lost STAT2, truncated and nonfunctional Tyk2, or impaired IFNAR are known. Papillomavirus E6 and E7 inhibit IFN production in transformed cells or E7/E7 transgenic mice as well as in transfected mononuclear and NK cells [84,85]. Cells with lost STAT1 might be resistant to both the antiproliferative and antiviral effects of IFN but contradictory observations exist as well about a direct connection between resistance and STAT1. A probable explanation lays in the expression of specific ISGs [80,86]. Interferon regulatory factor-1 (inducer of IFN␣ and IFN␤) is a tumor suppressor gene; IRF-1 expression reverts the oncogenic phenotype of NIH3T3 cells transformed by c-Ha-ras and c-myc [87]. No oncogene cooperation is needed in IRF-1(ⳮ/ⳮ) cells because full transformation may be achieved with the single Ha-ras oncogene [88]. Expression of IRF-1 diminishes with the progression of endometrioid carcinoma from Grade 1 to 3 [89]. In myelodysplastic syndromes and acute myelogenous leukemia, IRF-1 is truncated by skipping exons 2 or 2-3 [90]. Matrix metalloprotease9 (MMP-9) expression by tumor cells promotes invasion and metastasis as well as angiogenesis by degrading collagens and laminin. Tumor necrosis factor-␣ induces MMP-9 expression through NF␬B, which is a transactivator of the MMP-9 promoter. Interferon inhibits the expression of MMP-9 through competitive binding of IRF-1 to NF␬B binding promoter sequences [91]. INF regulatory factor IRF-1 also regulates the expression of the IFN-inducer PKR (double-strand RNA activated protein kinase) through the activation of the ISRE element in its promoter region [92]. Thus, a disabled IFN system in tumor cells is essential for viral oncolysis. The Ras Connection Expression of mutated ras seemed to confer sensitivity to NDV oncolysis given that N-ras–transformed tumorigenic human fibroblasts become permissive to NDV infection, whereas normal human fibroblasts were 1000-fold less sensitive to the


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virus [42]. Because ras-specific antisense oligonucleotide treatment of melanoma cells did not abolish the oncolytic effect of NDV, obviously there are multiple pathways operating in tumor-cell killing (J. C. Horvath, unpublished data). The point mutations leading to ras oncogene activation are seen frequently in cancer. Reovirus takes advantage of the overexpressed Ras oncogene in killing cancer cells. In melanoma, the ras gene is frequently mutated [93]. A ras-effector homologue, the Ras association domain family 1 (RASSF1) protein is considered to be a tumor suppressor gene. The promoter region and a second region in the first exon of the RASSF1 gene is hypermethylated and its expression is suppressed or abolished in 55% of melanomas [94]. That multiple pathways intertangle in tumor cells, conferring sensitivity to NDV-mediated oncolysis, is supported by L. Klampfer’s work showing that, in colon cancer cells, the mutated Ki-ras inhibits the expression of STAT1 and 2. Consequently, the expression of all IFN␥-inducible genes, including the tumor suppressor gene IRF-1, is reduced and the tumor cells are nonresponsive to IFN [95]. In colon carcinoma cells with wtKi-ras, the STAT1 and 2 genes are silenced by hypermethylation, and these cells would not respond to IFN␣ treatment [96]. The phenotypic and genotypic changes just mentioned occur in tumor-derived cell lines but not universally, suggesting that either pathway can interchangeably function in viral oncolysis. There may be third or fourth, more universal, causes of sensitivity of tumor cells to NDV infection. Role of the dsRNA-Dependent Protein Kinase Double-stranded RNA is a product of viral replication, whereas it is seldom produced in normal cells. Doublestranded RNA-dependent protein kinase is a serin/theronin kinase activated by dsRNA or PACT, a stress-activated kinase [97]. Binding of dsRNA to the two dsRNA binding domains of PKR causes conformational changes and leads to dimerization and autophosphorylation of PKR. The activated PKR phosphorylates its target, the eukaryotic IF2␣. The phosphorylated

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eIF2␣ in turn makes a stable complex with and inactivates the eIF2 complex and blocks initiation of protein synthesis. Double-stranded RNA-dependent protein kinase has a role in cell differentiation; it is also antiproliferative and pro-apoptotic [98]. The activated PKR phosphorylates and marks I␬B for ubiquitination and destruction, unmasking the nuclear localization domain of NF␬B. Nuclear factor-␬B is transferred to the nucleus, where it binds to the extended promoter sites of target genes [99]. The stress-activated kinase PACT is expressed in all tissues at low level, except in the apical part of the colonic villi, where epithelial cells stop cycling and are prone to A upon stress effect [100]. These cells also show high levels of phosphorylated (active) PKR and eIF2␣ (inactive) showing inhibition of protein synthesis. The stress-activated kinase PACT activates PKR by heterodimer formation even without dsRNA binding. Because of this heterodimer formation and consequent conformational changes, the PKR ATP binding site opens and PKR becomes phosphorylated [101]. Infection with NDV infection induces PACT and the protein becomes associated and co-localized with the viral N protein, and probably is involved as a host factor in the viral replication process. The stress-activated kinase PACT also activates target genes (like IFN␤) by activating NF␬B, IRF-3, and IRF-7 [102–104]. Apoptosis induction by activated PKR is executed through the activation of p38 mitogen-activated protein kinases (MAPKs), stress-activated protein kinases/c-Jun aminoterminal protein kinases. These kinases are all activated through TNF␣ signaling as well as by lipopolysaccharide (LPS) and dsRNA [105]. Double-stranded RNA-dependent protein kinase is co-localized and interacts with the A signal-regulating kinase-1, which interaction does not require the kinase activity of PKR [106,107]. In PKR ⳮ/ⳮ fibroblasts, however, poly(I)-poly(C) or LPS could not induce MAPK activation, showing that MAPK activation and A induction by these agents depend on PKR [105]. Influenza virus (and probably NDV) dsRNA-activated PKR induces Fas expression, making cells susceptible to FasL expressed by cytotoxic lymphocytes [108–110].


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Role of the Immune System Macrophages (M⌽) may exert cytotoxic effects or augment tumor growth [111–113]. Newcastle disease virus-infected M⌽ express nitric oxide and TNF␣ and demonstrate cytostatic and cytotoxic activity against a broad range of tumor cell lines. Intravenously transferred NDV-infected M⌽ suppressed lung metastases in lung tumor and breast cancer models, whereas noninfected M⌽ had no effect or even augmented tumor growth [114]. In NDV-infected mouse cells, the chemokine RANTES (regulated on activation, normal T cell- expressed and secreted) is induced [115–117]. The induction of RANTES does not require viral nucleic acid or protein synthesis and can be achieved by using ultraviolet-inactivated virus as well. Apparently virus binding is sufficient to induce signaling. Interaction of the NDV Ulster strain with the immune system is extensively discussed by V. Schirrmacher in Chapter 4 of this volume. NEWCASTLE DISEASE VIRUS THERAPY OF HUMAN CANCER The efficacy of NDV in killing xenografted human tumors in the mouse is very impressive [42]. Results of clinical trials to treat metastatic cancer with NDV, however, are much less encouraging. Furthermore, the virus strains used, dosage, and the method and frequency of application are different and the results are difficult to compare. The Lorence group studied extensively the oncolytic properties of the 73-T strain (which is a lytic NDV strain, vide supra) in mouse tumors and xenotransplanted human tumor tissues [43]. In their Phase I clinical trial, however, the isolate PV701 was used, derived from the ‘‘naturally attenuated MK107 vaccine strain’’ with plaque purification; no further reference on the parental strain was given [118,119]. Intravenous application of single or multiple doses from 1.2 ⳯ 1010 to 1.2 ⳯ 1011 PFU were tolerated well, although grade 1 and 2 toxicity occurred often, with fatigue, flu-like, and gastrointestinal symptoms being the most frequent side effects. Tumor

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site-specific toxicity also occurred and was treated with medication. Because toxicity occurred less often after the repeated virus application, a first injection of 1.2 ⳯ 1010 PFU PV701 was used for ‘‘desensitization.’’ Higher doses were associated with clinical responses: Of 79 patients treated (23 colorectal, 9 pancreatic, 9 renal, 8 breast, 8 non–small-cell lung, several other cancers, and sarcomas), 1 complete remission (CR; a tonsillar squamous cell carcinoma) and 1 partial remission (PR, a colon cancer) were observed and 14 patients showed no progression (4 to 30Ⳮ months’ duration). Histological examinations of tumor tissues showed inflammatory infiltrations. The question arises whether multiple viral cycles occur in infected tumor cells or whether virus-induced A is responsible for the cell killing. Why is it necessary to give such a megadose of virus if it is replicating in tumor cells? An even more important but unanswered question is whether or not the repeated large inocula of the virus induce tolerance or ‘‘immune paralysis,’’ allowing persistence of the virus [120]. A Hungarian group used an attenuated NDV veterinary commercial vaccine strain (re-named MTH-68/H) to treat various tumors in the forms of inhalation. Unfortunately, the claimed high response rate is supported only with anecdotal case presentations [121]. Repeated application of MTH-68/H induced MRI-documented PR (95% shrinking) in a 14-year-old boy with glioblastoma but was reported without histological proof [122]. Our clinical trial with the 73-T strain, approved by the institutional review board of the hospital, also gave mixed results. Let our patient populations be represented here by two cases: one a dramatic but temporary response to direct intratumoral NDV inoculation; the other, characterized by relentless growth of melanoma, despite various forms of viral inoculations. A single intratumoral injection of 107 PFU NDV into the primary melanoma invading the right nasal cavity and the maxillary sinus of a female patient was followed by days of sloughing of necrotic dark brown tissue and resulted in more than a 90% reduction of the tumor 2 months after NDV inoculation. The ‘‘thickened tissues’’ remained in the apex of the nasal cavity, but were negative for melanoma cells by biopsy.


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Three months later, the patient relapsed and repeated injections of the virus did not change the course of advancing disease. Would have a higher dose or repeated applications of the virus resulted in a better outcome? Or could surgical removal of the residual tumor, if any, after PR was achieved, have prevented relapse? A primary malignant melanoma on the left forearm of a 53-year-old man was surgically removed and his axillary lymph nodes with metastases were dissected. The patient refused the IFN␣2b protocol but received allogeneic NDV (73-T) oncolysate vaccine instead. He relapsed and local recurrences were removed and he accepted and completed the 1-year IFN protocol. He relapsed again in the epitrochlear lymph node and in-transit metastases appeared on his left upper arm, extending to the left chest wall. Some nodules were injected with dacarbazine or vinblastine and granulocyte-macrophage colony stimulatory factor (GM-CSF) with the hope of generating antigen-presenting dendritic cells (DCs) and in situ vaccine effect by the apoptotic tumor cells. Low-dose IL-2 was given subcutaneously to help raise tumor-specific lymphocytes. None of his nodules regressed. A melanoma cell line established earlier from one of his surgically removed melanoma lesions was killed by NDV inoculation in vitro. He and his family decided then to have some of the nodules injected with purified live 73-T NDV. The injected nodules became red and indurated but the rapid growth of both injected and surrounding nodules continued unchecked. No apoptotic tumor cells were observed in the fine-needle aspirates. Biochemotherapy (vinblastine, cis-platin, and dacarbazine; IFN␣2b; IL-2) and adoptive lymphocyte therapy with tumor-infiltrating lymphocytes, and lymphokine-activated killer cells were unsuccessful because his lung and liver metastases advanced. He developed brain metastases and died [123]. One can again speculate why the tumor cells failed to respond to virus injection. Because of the NDV oncolysate vaccination, he had virus-specific T cells, NK cells, and antibodies. Why did virus-specific antibodies not induce an antibody dependent cell mediated cytotoxicity (ADCC) type reaction against the virus-infected tumor cells? Why did viral oncolysate (VO) vaccines fail to reactivate his pre-existing mela-

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Figure 1 Co-culture of a human melanoma cell line with autologous tumor-infiltrating lymphocytes. Left side of the panel shows lymphocytes, free or attached to large tumor cells, stained with Annexin V and propidium iodide (PI) to detect apoptosis (A). Most tumor cells and some lymphocytes show the sign of late A with PI staining. Healthy lymphocytes, not killed by tumor cell counterattack, are marked with arrows on the right side of the panel (same cells illuminated by visible light).


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noma-specific immune memory cells? Could the lymphokines and growth factors released locally in the inflammatory reaction support tumor cell growth? It is known that melanoma and other tumor cells can turn the IL-2→IL-2 receptor or even the apoptotic FasL→Fas system to their own advantage as an autocrine loop, while avoiding apoptotic death [124,129]. Tumor cells producing FasL can kill attacking FasⳭ cytotoxic T lymphocytes and escape immune surveillance (Figure 1). Are we the only ones who observe such an unabated tumor growth coincidentally with VO application? Are the patients with progressive disease in clinical trials analyzed for unexpected rapid growth rate after intervention or just excluded from further treatment? In China, colorectal cancer patients were treated with autologous NDV oncolysate vaccine using the lentigenic La Sota strain. Patients without available surgical sample received NDV injection intradermally [130]. The median survival period for 310 vaccinated patients after resection of colorectal cancer was 5.13 years, vs. 4.15 years for 257 patients with resected tumor but no vaccination. The 5-year survival rate was 80% for patients with positive skin test after vaccination. Virus inoculation to tumor resulted in five stable disease (SD) in six patients with stomach cancer. One CR, three PR, and eight SD occurred in 13 patients with colorectal cancer. Toxic effects were not serious, represented by flu-like symptoms and fatigue. POSTONCOLYTIC TUMOR IMMUNITY After virus-induced oncolysis, mice acquire tumor-specific immunity (postoncolytic tumor immunity) and develop resistance to challenge with the same but virally not infected tumor [131,132]. The phenomenon of postoncolytic immunity is not clearly understood. Newcastle disease virus infection of tumor cells changes expression of cellular proteins. The expression of MART-1/Melan A melanoma-specific antigen is augmented four times upon NDV infection (Figure 2). Heat shock proteins (hsp) are stress-induced chaperones capable of binding and presenting antigen-specific peptides to antigen-presenting

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Figure 2 Expression of MART-1/MELAN protein in mock- or NDVinfected human melanoma cell line at 37⬚C or 43⬚C Western blot with MART-1 specific antibody, chemiluminescence.

Figure 3 Expression of hsp70 protein in mock- or NDV-infected human neuroblastoma and melanoma cell lines at 37⬚C or 43⬚C. Western blot with hsp70-specific antibody, chemiluminescence.


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cells (APC) and tumor-specific peptides are among them. Newcastle disease virus infection induces expression of hsp in natural host chicken cells and in infected tumor cells (phosphorylated hsp27) [133]. We observed induction of hsp70 and hsp90 in NDV-infected melanoma and neuroblastoma cell lines (Figure 3). By binding to their ligand CD40, hsp induce DC maturation [134,135]. Viral oncolysate vaccines contain live NDV, which, in turn, induces the production of IFN␣, IL-15, and TNF␣ in the infected tissues upon vaccination [116]. VIRAL ONCOLYSATE VACCINES W. Cassel started his clinical trial with NDV 73-T oncolysate adjuvant vaccine in patients with surgically resected melanoma with lymph node metastases in the mid-1970s [136,137]. To have most possible melanoma-specific antigens represented, several melanoma cell lines were rotated in the vaccine consisting of three cell lines in a given injection with no chemical or biological adjuvants. One allogeneic cell line was substituted with autologous melanoma cells when available. The vaccine contained live NDV. All patients alive still continue receiving vaccination. The efficacy of the vaccine was compared with historical controls; the patients were not prospectively randomized. The trial gave an unprecedented over-60% survival rate after 10 years and 55% after a 15-year followup, whereas only 27% of nonvaccinated patients are alive relapse-free [138,139]. The 20-year evaluation of VO-vaccinated patients of W. Cassel is published in this volume. Our VO adjuvant melanoma vaccine program with NDV 73-T uses allogeneic melanoma cells developed in our laboratory from autologous or surgical resections. Each vaccine contained oncolysates from three cell lines. The patients received 26 vaccinations, the first eight in weekly intervals, followed by biweekly injections. One allogeneic cell line was substituted with autologous tumor cells, when available. Since 1999, patients are randomized to receive low-dose IL-2 or IFN␣2b subcutaneously and the vaccine is admixed with GM-CSF (250 ␮g). We observed early relapses during vaccination with both

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Figure 4 Expression of recombinant hemagglutinine-neuraminidase protein (HN) in human bronchioalveolar carcinoma (B) and melanoma (C,D,E and F) cell lines (established in our laboratory). The cells were stained 24 hours after transfection with rabbit polyclonal antibody against Newcastle disease virus and FITC (fluorescein isothiocyana) conjugated anti-rabbit IgG (A-D) or photographed after hemagglutination with chicken red blood cells (E,F). The bronchioalveolar carcinoma cells in A are transfected with the control plasmid without HN; cells in B–F were transfected with an eukaryotic expression vector carrying the HN gene. Cells on D were selected by hemagglutination on a chicken red blood cell monolayer chemically attached to a tissue culture flask (every cell tests positive for HN by immune fluorescence).


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vaccines (with or without lymphokines). With the first NDV oncolysate vaccine without lymphokine adjuvants, 63% of the patients (13/15 patients with Stage IIB, 11/21 with Stage III and 1/4 with Stage IV disease) finished the whole course; 34% discontinued vaccine treatment because of early relapse. Of patients who finished the vaccination, 64% are free of disease (4 to 7 years postvaccination). Patients with Stage IV disease did not benefit from the vaccine. Why are our results inferior to the published exceptional results of the W. Cassel trial? Early clinical relapses occurred in patients who were accepted on the protocol on the patient’s demand; or because of leniency, despite the fact that some patients were already in the progress of subclinical relapse when entering the program. Therefore, we recognize that [1] Viral oncolysate-induced antitumor immunity develops slowly; and [2] the VO is not a therapeutic vaccine. It may be effective against dormant micrometastases, but it is ineffective against growing and progressive disease. We cannot explain why VO fails to mobilize promptly pre-existing antitumor memory cells. For the valid evaluation of new treatment protocols, the comparison of a prospectively randomized group of patients treated differently is considered to be the most reliable. For the virotherapy of cancer, such protocols seldom have been applied. It is part of medical history that matched historical controls were used for the evaluation of new treatment protocols. For example, in the BCG (Bacillus Calmette-Gue´rin) of cancer immunotherapy, such control groups were widely relied upon. Clinical investigators who used ‘‘matched historical’’ controls remained as respected heads of departments in leading cancer institutions worldwide. The practice has not been abandoned or condemned. However, a biased selection of matched historical controls weakens the control group and renders the treatment group appear artificially improved. We refrain from such a comparison. However, our VO-vaccinated patients were enrolled with adverse prognostic signs and by the natural history of melanoma they were expected to relapse in 70% to 80% of the cases. We did not selectively enroll patients with favorable prognostic signs to artificially improve the results of the VO vaccination program.

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In Germany, the Atzpodien group used irradiated autologous or allogeneic tumor cell oncolysates made with the 73-T strain of Cassel and used it together with low-dose subcutaneous IL-2 and IFN␣ in an adjuvant setting to protect patients with renal cell carcinoma from recurrence [140]. The ongoing Phase II clinical trial involved 208 patients at the time of the report. Of these, 15% relapsed locally or with lymph node and distant organ metastases; the median survival was 21 months (range 2–64 months), but no further follow-up is available [141]. Testing the tumor-specific cellular and humoral immune responses of vaccinated patients, no tumor-specific antibody or increase in cytotoxicity was found. As an effect of the vaccine, the level of TNF␣ and IFN␥, but not of IFN␣, increased in the serum [142]. The Schirrmacher group in Germany used the non-lytic Ulster strain of NDV to produce adjuvant vaccines for clinical trials of various malignancies. Detailed evaluation of the clinical trials of V. Schirrmacher’s group can be found elsewhere in this volume. There are basic differences between their adjuvant vaccine and the lysate vaccines. The lysate vaccine contains soluble components and fragments of tumor cell membranes and live NDV (free and membrane bound), whereas the Schirrmacher vaccine contains intact tumor cells with viral particles fused to the cell membrane. The more intact and viable the tumor cells were, the more efficacious was the vaccine [143]. Virus infection of the tumor cells leads to upregulation of HLA-DR molecules, IFN␤, and the chemokines RANTES and IFN␥-inducible protein-10. The infected tumor cells then die of A. Apoptotic bodies of tumor cells are phagocytosed by APC to present tumor antigens and thus generate immune T cell clones [116]. Newcastle disease virus oncolysate adjuvant vaccination of patients with glioblastoma multiforme increased delayedtype immune reactions and caused no serious side effects, but no improvement in survival was observed [144]. SAFETY Genomic RNA synthesis of NDV is error-prone because of the lack of 3′-5′ exonuclease ‘‘proofreading.’’ However, new virus


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strains evolve in nature slowly because most of the mutations in nucleic acid sequence cause no changes in amino acid sequences or might result in lethal virus mutants that are never detected [145,146]. At Emory University, Atlanta, GA, more than 12,000 injections with 73-T oncolysate vaccines containing live virus did not result in the appearance of any new or more pathogenic virus variant and did not induce any disease in the patients, in livestock, or among wild birds. Attempts to recover live virus from the blood, saliva, and urine of vaccinated patients by W. Cassel or us were unsuccessful. The mega-doses applied by the Lorence group for oncolytic treatment resulted in transient excretion of infectious virus and require further considerations [119]. FUTURE DIRECTIONS It is clear from past and present clinical trials with NDV as an oncolytic virus that complete remissions of metastatic disease seldom occur and the natural course of malignant diseases stabilizes, but without cure. Tumor cells could become resistant to repeated applications and these selected clones grow out in relapses or in progressive disease. Producing a better, more oncolytic yet safe agent is on the wish-list of everyone working on the fast-growing field of virotherapy. Selection of more efficient oncolytic variants on specific target cells by mutagenesis can give such results. A melanoma-specific NDV variant was developed from the Ulster strain, however, no further trials are known to show its usefulness [147]. Modifying viral proteins to increase specificity with targeted mutations might be more fruitful when we know the mechanism of action more accurately. The NDV hemagglutinin by itself is an IFN inducer and strong antigen [148,149]. It can be expressed in tumor cells from encoding eukaryotic expression vectors (Figure 4) [149–152]. In our experiments, the rHN (cloned cDNA was ´ va Nagy, University of Guelph, Ontario, Cankind gift of Dr. E ada, further subcloned into an eukaryotic expression plasmid vector) was found mostly in the cytoplasma but was also ex-

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pressed on the cell membrane, making it possible to select HNtransfected cells with hemagglutination (Figure 4D) [153]. The vector could also encode a cytokine adjuvant gene such as GMCSF. Can vector-expressed NDV HN substitute for live NDV oncolysis to make virus (antigen)-modified tumor vaccine? Several NDV strains are fully sequenced and the viral proteins and their function are well characterized. The relative genomic stability of NDV makes it a good candidate as a virus vector to carry genes encoding antigens of other pathogens or tumor [154,155]. Because of the modular structure of the viral genome, foreign genes can be inserted between viral protein coding regions without a major negative effect on the virus replication [156,157]. Would an oncolytic, lymphokine-armed NDV be more efficacious in generating protective immune response, or attract more NK cells or cytotoxic T lymphocytes to amplify the tumor cell killing and protect from later relapses? Can we make tumor cell-targeted NDV by changes introduced in the HN protein [158]? Until we achieve this goal, we are to use the naturally oncolytic NDV, not necessarily as a therapeutic, but as an adjuvant antitumor vaccine. Single-agent therapy to treat malignant diseases is rarely successful, whereas multi-agent treatments show additive or even synergistic effects. Would viral oncolysis be more efficacious if different oncolytic viruses were applied in an alternating fashion? Recent drugs coming from extensive translational research and as spin-offs of the human genome project cannot be ignored. They are often more targeted, cause fewer side effects than presently used chemotherapeutic agents, do not induce host immune reactions, and do not replicate in the host. These agents could and should be combined or alternated with VO therapy. This subject is extensively discussed by J. G. Sinkovics elsewhere in this volume.

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6 Influenza A Viruses with Deletions in the NS1 Gene—a Rational Approach to Develop Oncolytic Viruses MICHAEL BERGMANN Department of Surgery, University of Vienna Medical School Vienna, Austria THOMAS MUSTER Department of Dermatology, University of Vienna Medical School Vienna, Austria

THE PRINCIPLE OF INFLUENZA A VIRUS MEDIATED ONCOLYSIS The major feature typical of oncolytic viruses is their conditionally replicating phenotype, which permits them to grow in malignant cells but not in normal tissue. The recent elucida575

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tion of the function of the influenza virus NS1 protein [1] gave us the possibility for a rational development of oncolytic influenza A viruses by virtue of genetic engineering. The antagonism of the cellular antiviral type I interferon (IFN) response turned out to be one of the main functions of NS1. This finding is based on the observation that influenza A viruses, which lack a functional NS1 gene, do not grow in IFN-competent systems but replicate effectively in systems that lack expression of functional IFN [2], contain defects in the Jak/STAT (signal transducer and activator of transcription) pathway [3], or lack expression or activation of the IFN-induced, dsRNA activated protein kinase (PKR) [4]. The link between influenza A virus NS1-deletion viruses and oncolysis derives from the observation that tumor cells frequently contain defects in the IFN pathway [5] as well as in PKR activation [6]. As a consequence, NS1-deletion mutants are capable of selectively destroying such tumor cells. This renders genetically engineered NS1-deletion viruses prototypes for oncolytic influenza A virus strains. Developments that led to genetically modified oncolytic influenza virus strains, the general biology of the virus, its interactions with the IFN system, and the required characteristics of the target tumor are described in this chapter. CHARACTERIZATION OF THE VIRUS Influenza A virus is a segmented negative-strand RNA virus. It contains a lipid envelope anchoring the hemagglutinin (HA), neuraminidase (NA), and an iron channel, the M2 protein. The matrix protein M1 forms a protein layer beneath the envelope. The core of the virus is inside the M1 protein layer. It consists of ribonucleoprotein complexes (RNPs), which contain genomic RNA molecules associated with the nucleoprotein (NP) and the viral polymerase subunits PB1, PB2, and PA. In addition to these eight viral structural proteins that form the virus, two more proteins—the nonstructural protein (NS1) and the nuclear export protein (NEP)—are encoded by the genome [1]. According to some reports, the NEP is also present in virions

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[7,8]. Recently, influenza A virus was found to encode one more protein, PB1-F2 [9]. Thus, the influenza A virus is a fairly small virus. Its limited number of proteins are well characterized. This is certainly desirable for a virus to be used for virotherapy. The fact that influenza A virus is an RNA virus excludes the possibility of the virus being incorporated in the host genome, which would be an unwanted side effect. CHARACTERISTICS OF THE GENOME The genome of influenza A virus consists of eight different RNA molecules. Each RNA segment encodes one viral protein except for the PB1, M, and NS RNA segments, which encode two proteins, PB1 and PB1-F2, M1 and M2, and NS1 and NEP, respectively. Because the genomic viral RNAs (vRNAs) are of negative polarity, they have to be transcribed into mRNA before the viral proteins can be synthesized. This transcription is performed in the nucleus of the infected cell by the incoming viral RNA-dependent RNA polymerase, a trimeric complex formed by the PB1, PB2, and PA proteins. This viral polymerase is also responsible for the replication of the vRNAs. During replication, the viral polymerase makes complementary copies (cRNAs) of the vRNAs. These cRNAs, in turn, are used as templates by the viral polymerase to generate new vRNAs. Both vRNAs and cRNAs are found associated with the viral NP protein. During transcription, mRNAs instead of cRNAs are generated from the vRNA templates. All eight vRNA segments contain short 3′ and 5′ non-coding regions flanking their internal coding sequences. These non-coding regions contain cisacting signals required for the replication, transcription, and packaging of the vRNAs into virus particles [10,11]. The single segments can be exchanged by any two viruses if they infect the same cell. This property of the virus is important if genetically manipulated viruses should be used in humans. A genetically modified influenza A virus segment can be incorporated by reassortment into the circulating wild-type strain. For this reason, the genetic change preferably should be linked to an attenuation marker within the same segment.

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INTRODUCING MUTATIONS INTO THE GENOME OF INFLUENZA VIRUS Reverse genetics was a prerequisite to obtain conditionally replicating oncolytic influenza viruses. These techniques, which permit site-specific genetic manipulation of influenza virus, were first established by P. Palese’s group [12]. In the initial experiment, in vitro reconstituted NA-specific RNPs were transfected into cells that previously had been infected with a helper influenza A virus [13]. This method was further developed by intracellular reconstitution of RNP complexes derived from plasmid-based expression vectors. In this system, influenza virus RNA transcripts are derived from plasmids that are transfected into cells. When cells infected with helper virus are cotransfected with conventional eukaryotic proteinexpression plasmids expressing the viral polymerase proteins PB1, PB2, PA, and NP, the intracellularly reconstituted RNPs are taken up into new infectious viruses. Contrary to the RNP-transfection system, the plasmidbased transfection system eliminates the need to purify the viral NP and polymerase proteins required for in vitro reconstitution of RNP complexes [14]. A breakthrough in the field came with the establishment of entirely plasmid-based techniques to rescue influenza viruses in the absence of helper viruses [15,16]. These techniques are based on the method of intracellular reconstitution of RNP complexes just described. Cells are cotransfected with two subsets of plasmids. The first includes eight polymerase I RNA-expression plasmids, each encoding one individual influenza virus vRNA. The second subset includes at least four polymerase II protein-expression plasmids encoding the PB1, PB2, PA, and NP proteins. These viral proteins encapsidate and initiate transcription and replication of the eight vRNAs, mimicking intracellular replication during naturally occurring influenza virus infections. Consequently, cells transfected with the complete set of 12 plasmids produce infectious influenza viruses subsequently infect cells and generate more viruses. As a result, high titers of recombinant influenza viruses are obtained. The generation of genetically manipulated virus entirely from plasmids might be of


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major importance for the application of such a virus to humans because it facilitates generating the virus under good laboratory practice conditions. Establishing reverse genetics techniques to genetically manipulate influenza virus genomes has revolutionized the research field of influenza viruses. These techniques were used to analyze the functions of influenza virus proteins and RNAs. Analysis of the function of the influenza virus NS1 protein was the basis for generating conditionally replicating oncolytic influenza virus strains subsequently described. THE DELNS1 VIRUS The prototype of an oncolytic influenza A virus is a genetically engineered virus that lacks the NS1 protein. The first NS1deletion viruses were generated by A. Egorov and colleagues. Surprisingly, these deletion mutants grew to wild-type titers in Vero cells, but were attenuated in Madin Darby Canine Kidney (MDCK) cells [2]. A NS1-knockout influenza A virus (delNS1 virus) was then obtained by replacing the wild-type NS gene with a genetically engineered intron-less NS gene, which can only direct the expression of the NEP protein from its unspliced mRNA. Analysis of the replication properties of this virus allowed defining new functions of the NS1 protein [3], a nonstructural viral protein expressed in high levels in infected cells but not in the virus. Previously, the NS1 protein has been associated with several functions during viral replication—e.g., the inhibition of host mRNA polyadenylation [17], splicing [18,19,20] and nucleocytoplasmic export [18,9], the inhibition of the IFN-inducible antiviral enzyme PKR [21,22,23], and the enhancement of mRNA translation [24], with a higher specificity for viral mRNA [25,26,27]. Despite all the multiple functions that have been ascribed to the NS1 protein, the most obvious characteristic of the delNS1 virus was its conditionally replicating phenotype. The virus was highly impaired in the ability to grow in MDCK cells, 10-day-old embryonated eggs or wild-type mice, but it replicated to titers close to wild-type virus in Vero cells and

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6-day-old embryonated eggs, as well as STAT1-knockout cells and STAT-knockout mice. The facts that Vero cells have lost functional expression of their type I IFN genes; 6-day-old embryonated eggs, but not 10-day-old, have an immature-type IFN system and STAT1 is a key protein in the IFN pathway, all indicated that the NS1—in addition to the previously observed functions—is an IFN antagonist. THE INTERFERON PATHWAY AND THE NS1 PROTEIN The cellular signal cascade to type I IFNs is initiated by the binding of IFN to its receptor (IFN-AR) [28]. Despite the fact that IFN induces more than 300 different genes in the cell, the IFN signal from the cell surface to the nucleus is mediated by only a few proteins involved in the Jak/STAT pathway. Associated with the intracellular domain of the IFN-receptor are two protein kinases, Jak1 and Tyk2, which are activated upon receptor binding. The signal transducers and activators (STATs) are then recruited to the receptor complex and activated through posphorylation. Signal transducers and activators of transcription STAT1, STAT2, and p48 lead to the formation of the transcription complex ISGF-3, which translocates to the nucleus and promotes the transcription of IFN-responsive genes that have the IFN-responsive signal elements within their promoter regions. The antagonistic effect of NS1 in the IFN pathway was pinpointed by the fact that the delNS1 virus grew to titers similar to wild-type virus in STAT1 knockout mice [3]. Among numerous IFN-responsive genes, some of the essential proteins for the IFN-induced antiviral response are the dsRNA-activated protein kinase (PKR), MxA, and 2′-5′ oligoadenylate synthetase (OAS). Activation of both PKR and OAS results in blockage of translation. Thus, one of the endpoints of the IFN-mediated signal cascade is the inhibition of translation. Further characterization of the NS1 knockout virus revealed that the NS1 protein of influenza A virus is clearly involved in prevention of the activation of PKR, therefore inhibiting PKR-induced translational blockage in infected cells [4].


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In addition, the NS1 protein prevents the activation of other dsRNA-activated cellular pathways, such as the activation of transcription factors involved in the induction of type I IFN expression [29,30]. Because the NS1 protein is a dsRNAbinding protein, it is tempting to speculate that inhibition of the IFN system by the NS1 is mediated by its ability to bind dsRNA, a potent activator of the IFN antiviral response. Indeed, the NS1 dsRNA-binding domain of the NS1 protein appears to be the main domain responsible for its type I IFNantagonistic properties [29,30]. Because its IFN antagonist is eliminated, the NS1 knockout influenza A virus grows selectively in cells with deficiencies in the type I IFN system. Because a large number of tumor cells have an impaired type I IFN response, this mutant influenza A virus replicates in the majority of cell lines derived from tumors. Given the cytopathic nature of influenza virus, replication of the NS1 knockout virus in tumor cells results in selective killing of these cells [31]. Selective oncolytic properties have also been demonstrated with other viruses that are restricted in growth because of their inability to inhibit the type I IFN system or the IFN-inducible PKR-mediated antiviral response [32,33], (for review see 34). TUMOR-ASSOCIATED DEFECTS OF THE INTERFERON PATHWAY Given the elimination of its IFN antagonist, the NS1 knockout influenza A virus selectively grows in cells with deficiencies in the type I IFN system. Because a large number of tumor cells have an impaired type I IFN response, the delNS1 virus fails to replicate in normal cells but replicates in the majority of tumor-derived cell lines. Defects in the IFN pathway involve a number of different proteins. Defects in the Jak/Signal Transducer and Activator of Transcription Pathway Interferon resistance appears to be a general phenomenon in malignancies such as malignant melanoma, hematological

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malignancies, and carcinoids. The most frequently observed defects that lead to IFN resistance are alterations in proteins of the Jak/STAT pathway because defects in this pathway cannot be bypassed by an alternative signal cascade. The central transcription factor ISGF-3, which consists of STAT1, STAT2, or p48, is most often affected. For example, in melanoma cell lines, alterations of ISGF3 components correlated with IFN non-responsiveness, including a lack of constitutive expression and a lack of activation of these factors [5,35]. The most frequent defect observed in the resistant cell lines was lack of STAT1 protein expression. This observation was extended to cell cultures established from melanoma patient biopsies. Other defects such as a reduced phosphorylation of Tyk2, a tyrosine kinase that binds to the intracellular part of the IFN receptor, have also been reported [35]. However, resistance to IFN can also result from defects of IFN-stimulated genes (ISGs). Similar to melanomas, chronic myeloid leukemia cells resistant to IFN-␣ also lack STAT1 expression [36]. Because IFN is used as a therapeutic regimen for carcinoids, protein expression of STATs was also investigated in this type of cancer [37]. Tissue immunostaining of STAT1 and STAT2 demonstrated that STATs were significantly increased during IFN-␣ treatment. The same was observed for leukaemia. Induction of STAT1 by IFN treatment was only observed in patients with objective response as well as in patients with stable disease, but not in those with progressive disease. This supports the clinically relevant role of the Jak/STAT pathway and, at the same time, indicates the need of an alternative therapy for IFN-resistant cancers. Defects in Protein Kinase The other group of IFN pathway-associated defects relevant for virus-induced oncolysis is the inhibition of PKR activation by an oncogene. L. J. Mundschau and D. V. Faller demonstrated that dsRNA-mediated activation of PKR is blocked in v-ras–containing cells in a manner specific to ras [6]. This inhibitory effect of ras was not attributable to the transformed


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phenotype. A heat and phenol chloroform-sensitive PKR inhibitory activity could be demonstrated in these cells, that functions in trans when mixed with untransformed cell extract prior to stimulation with dsRNA. Thus, even though other functions of the IFN-pathway remain unaltered, the antiviral effect of IFN-induced PKR, which we had proven to be most relevant in the IFN pathway, is inhibited by oncogenic ras [4]. The ras-mediated inhibition of PKR activation is of major importance for a broad range of malignancies, because oncogenic ras has been found in approximately 30% of human tumors. In fact, in pancreatic carcinoma, one of the carcinomas with a very poor overall prognosis attributable to the lack of adequate chemotherapy, ras mutations occur in more than 90% of the tumors. In other frequent cancers, such as lung or colon cancers, oncogenic ras is found in 40% and 50%, respectively. In malignant melanoma, this oncogene is activated in approximately 30% of the cases. A reduced PKR activity might not be limited to cancer cells expressing oncogenic ras. For example, although expressed at high levels, PKR activity appears to be severely attenuated in several breast cancer cell lines, as judged by its ability to phosphorylate eIF-2a (Savinova, 1999). INFLUENZA A VIRUS MEDIATED ONCOLYSIS IN IFN RESISTANT TUMORS Because the delNS1 virus grew in IFN-defective systems as such STAT1-knockout mice, we hypothesized that it might also replicate in IFN-defective tumor cell lines. Different tumor cell lines derived from melanomas, hepatomas, and teratocarcinomas were analyzed. Growth of the delNS1 knockout virus in these cell lines correlated with IFN resistance (current authors, unpublished). In the more IFN-sensitive cell lines, growth of the delNS1 virus was severely attenuated compared with the resistant cell lines. This further indicates that viral growth is mainly dependent on the IFN phenotype and is not restricted by the histological phenotype. Infection of IFN-sensitive cell lines at high Multiplicity of Infection (MOI) with the NS1 deletion mutant still resulted in

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lysis of the cell. Importantly, adding IFN completely inhibited the lytic effect of the delNS1 virus in these cells. In contrast, exogenous IFN was not capable to block viral infection in IFNresistant cells. We believe that the growth of the NS1-deletion mutants in the presence of IFN is relevant for the in vivo situation, given that the delNS1 virus is a potent inductor of IFN in normal cells. To further investigate the influence of factors secreted by stroma cells exposed to delNS1 virus, we infected an endothelial cell line with the delNS1 virus. This cell line does not permit productive replication of the delNS1 virus. Supernatants from the infected endothelial cells inhibited oncolysis in IFN-sensitive but not in IFN-resistant cells. This supports the dominant role of IFN on the inhibition of influenza A virus growth and indicates that the tissue cytokine response against the virus might be circumvented, if IFN-resistant cancers are taken as targets for influenza A-mediated oncolysis. We also tested the growth of a virus with a truncated NS gene coding for the NH2 terminal 99 aa (NS1-99 virus). This virus was also shown to be highly attenuated in mice, although the level of attenuation was lower than that of the delNS1 virus [38]. The NS1-99 virus still contains the RNA binding site located in a helix and comprising the 71 NH2-terminal aa. However, for efficient RNA binding, a dimerization domain, present in the carboxy terminal half of the protein, is also necessary [39]. Therefore, viruses such as the NS1-99, which only contain the NH2 terminal helix but lack a functional dimerization domain, should be attenuated in their RNAbinding capacity. We hypothesized that this phenotype should have retained partial antagonism of the IFN response. Indeed, the growth of the NS1-99 virus was less dependent on IFNmediated growth inhibition than the delNS1 virus. This correlates with the fact that the NS1-99 virus is less attenuated in mice than is the delNS1 virus. Analysis of the oncolytic potential of influenza A deletion viruses on subcutaneously established IFN-resistant tumors in the severe combined immune-deficient (SCID) mouse model revealed that the less attenuated NS1-99 virus was superior to the delNS1 virus. This indicates that efficient influenza A virus-mediated oncolysis can be hampered by overattenuation.


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However, the fact that the length of the NS1 deletion correlates with the level of attenuation provides the possibility to tailor influenza deletion mutants with the desired level of attenuation. At present, experiments are being performed to define the optimal-length NS1 protein, which mediates effective oncolysis and is sufficiently attenuated. INFLUENZA A VIRUS-MEDIATED ONCOLYSIS IN TUMOR EXPRESSION OF ONCOGENIC RAS Another defect in the IFN-associated signal cascade relevant for delNS1 virus growth results from ras-mediated inhibition of PKR activation. Patrick Lee’s group was the first who exploited this defect for virotherapy using reovirus. We reasoned that the delNS1 virus should also grow specifically on rasexpressing tumor cells given that we had previously demonstrated that the NS1 has an antagonistic function toward PKR activation and replicates in PKR-deficient systems. Indeed, Nras transfected cells supported delNS1 virus growth, whereas the parental cell line did not [31]. Abortive growth in the nonpermissive cell line was associated with activated PKR. Apparently, other IFN-induced proteins such as OAS or MxA did not prevent viral growth in these cells. These data show that nonpermissive cells become permissive upon transfection of oncogenic ras. Expression of oncogenic ras correlated with inhibition of PKR activation, which confirms the concept that oncogenic ras is an inhibitor of PKR activation. These data also confirm the hypothesis that PKR is one of the major antiinfluenza antagonists within the IFN pathway. Importantly, the delNS1virus induced a complete cytopatic effect (CPE) in the ras-positive cells even when infection was done at a low m.o.i., indicating multi-cycle replication. Even though no CPE was observed during infection of the nonpermissive wild-type cell line with the delNS1 virus at the low moi, at high moi, the virus still induced CPE. Obviously, infection of nonpermissive cells with the delNS1 virus leads to death of the infected cell, although no detectable virus is produced. The delNS1 virus-induced cell death might be me-

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diated by induction and activation of PKR, given that activated PKR has been shown to be associated with apoptotic cell death. The conditionally replicating phenotype of the delNS1 virus in ras-postive tumor cells translated to a therapeutic effect in a severe combined immunodeficiency (SCID) mouse model. In this approach, virus was administered by intratumoral injection. Virus replication specific for the tumor was confirmed by immunohistochemisty. We also analyzed whether the ras-dependent growth of the delNS1 virus was restricted to a certain tumor cell line or tumor type or whether this phenomenon was of general interest for other tumor entities. This virus also grew on other malignancies that contained ras mutations, such as lung carcinoma or hepatoma, again suggesting that influenza A virus growth is not restricted by histology, but by the molecular phenotype of the tumor. In contrast, in nonmalignant human cell lines, such as endothelial cell lines, amelanocytic cell lines, or primary keratinocytes, that are susceptible to wild-type virus infection, the delNS1 virus did not replicate, which underlines the apathogenic phenotype of the delNS1 virus. PROPERTIES OF INFLUENZA A VIRUS FOR VIROTHERAPY Influenza A virus derived preferentially from oncolytic strains have only been described very recently and still lack proof of their efficient and safe application in humans. However, we believe that influenza delNS1-deletion mutants have a number of properties that make this virus suitable as an oncolytic agent: (1) DelNS1 virus mutants are apathogenic (delNS1 virus) or highly attenuated (NS1-99) virus in normal mice [38]. Moreover, intratumoral virotherpy was associated with no side effects in SCID mice. Thus, these viruses should be well tolerated even in immunocompromised cancer patients. (2) The genetic change that promotes the preferential replicating phenotype in tumors is an attenuation marker. Thus, it is not possible to introduce a genetically engineered segment into a wild-type virus by reassortment because this segment would attenuate the virus and convert it in a live virus vaccine. (3) The apathogenic phenotype is attributable to a large deletion


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in its genome, which is unlikely to revert. It should be noted that attenuated influenza A viruses have been administered to humans for vaccine purposes with few adverse effects [40,41]. (4) Given that there are multiple serologically defined subtypes of influenza A viruses, different subtypes of the delNS1 virus can be constructed by exchanging the antigenic surface glycoproteins of the virus, the hemagglutinin, and the neuraminidase. The availability of modified delNS1 viruses may allow repeated administration of these oncolytic strains. Similarily, an existing immunity of the host can be circumvented by choosing strains with appropriate hemagglutinin and neuraminidase.(5) It is possible to construct influenza A viruses with shorter deletions in their NS1 protein. The length of the NS1 protein inversely correlates with the level of attenuation. This feature of the delNS1 virus permits us to choose the optimal length of the NS1 protein that is associated with efficient tumor destruction but is still sufficiently attenuated in the host to allow a safe application of the virus. (6) The delNS1 virus was shown to induce high amounts of NF-␬B [30], a key protein of the proinflammatory immune response. Thus, NS1-deletion virus-based virotherapy might be associated with an effective immune stimulation at the site of the tumor could lead to tumor destruction at a distant site by the stimulation of a specific antitumor immune response. A concern for the use of influenza A viruses as therapeutic agents is the possibility of causing a new epidemic by introducing a new viral strain to mankind. The antigenic epitopes that determine the serologic phenotype of the virus are within the HA and NA proteins. Clearly, the HA protein is immunologically more important. Major changes in HA and NA B-cell epitopes lead to antigenic shift; minor changes cause an antigenic drift. There exist 14 different serological subtypes of the HA protein, of which H1, H2, H3, and H5 are associated with human infections. Concerning the NA protein, two subtypes (N1 and N2) have occurred in humans. At present, two strains, H1N1 and the H3N2, are circulating. In Europe and the United States, influenza epidemics only occur during winter for reasons that are not elucidated yet. Each year, the virus slightly changes because of the antigenic drift. For this reason,

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the current vaccine formula is modified annually. Given that the new virus strains usually appear in Southeast Asia, a worldwide net is used to predict the phenotype to the annual viral strain and the vaccine formula. To prevent the possibility of introducing new strains in the circulation, we will incorporate the annual HA and NA proteins in the virus, used for oncolytic purposes. ONCOLYTIC REOVIRUSES Whereas the influenza NS1-deletion mutants were engineered to selectively replicate in IFN-deficient cells and cells expressing oncogenic Ras, reovirus a nonenveloped, double-stranded RNA virus—possesses inherent selectivity for tumor cells expressing ras. In fact, data on the connection among ras, PKR, and reovirus [42], and our own results showing that the NS1 protein of influenza virus counteracts the PKR-mediated antiviral response [4], led to the hypothesis that an influenza virus lacking the NS1 gene might selectively grow in cells with an activated ras-signalling pathway. For several decades, it was known that reovirus exhibited preferential cytotoxicity for transformed cells over normal cells. However, the mechanism for this selectivity was just discovered recently. Specifically, it was shown that NIH-3T3 cells, which are resistant to reovirus infection, became susceptible when transformed with activated sos or ras. Restriction of reovirus proliferation in untransformed NIH-3T3 cells was at the level of viral protein synthesis. Protein kinase, the phosphorylation of which inhibits translation, was phosphorylated in untransformed NIH-3T3 cells after infection with reovirus, but it was not phosphorylated in infected or uninfected transformed cells. Inhibition of PKR phosphorylation by 2-aminopurine, or deletion of PKR, led to enhancement of reovirus protein synthesis in untransformed cells. These results suggested that, unlike the case in untransformed cells, phosphorylation of PKR is blocked by elements of an activated ras pathway in the transformed cells, allowing viral protein synthesis to ensue and the lytic cycle to proceed. An activated ras-signalling pathway therefore appeared to be the basis of reovirus oncolysis [42].


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To investigate whether this property can be exploited for cancer therapy, SCID mice bearing tumors established from v-erbB–transformed murine NIH 3T3 cells or human glioblastoma cells were treated with the virus. A single intratumoral injection of virus resulted in regression of tumors in the majority of mice. Multiple treatments of immune-competent mice bearing tumors established from ras-transformed cells also resulted in tumor regression [33]. Subsequently, it was shown that reovirus also is capable of destroying different types of neoplastic cells in tissue culture and animal models. The result of these studies are summarized below: M.E. Wilcox and colleagues [43] showed that reovirus has potent activity against human malignant gliomas in vitro, in vivo, and ex vivo. Specifically, reovirus was capable of killing more than 80% of malignant glioma cell lines tested. It caused a dramatic and, often, complete tumor regression in vivo in subcutaneous and intracerebral human malignant glioma mouse models. Moreover, survival could also be prolonged. Reovirus was also able to infect and kill primary cultures of brain tumors removed from patients. It killed all glioma specimens but none of the cultured meningiomas tested. The feasibility of using reovirus as an agent against human colon and ovarian cancer was also evaluated. It was observed that reovirus efficiently infected all human colon cancer cell lines and human ovarian cancer cell lines tested, but did not infect normal colon or ovarian cell lines. Ras activity in the human colon and ovarian cancer cell lines was elevated compared with that in normal colon and ovarian cell lines. In animal models, intratumoral as well as i.v. inoculation of reovirus resulted in significant regression of established human colon and ovarian tumors implanted at the hind flank. Histological studies revealed that reovirus infection was restricted to the tumor. Moreover, in an intraperitoneal human ovarian cancer xenograft model, inhibition of ascites tumor formation and the survival of animals treated with live reovirus were significantly pronounced. Reovirus infection in ex vivo primary human ovarian tumor surgical samples was also confirmed, further demonstrating the potential of reovirus therapy. These results suggest that reovirus holds promise as

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a novel agent for human colon and ovarian cancer therapy [44]. P. Lee’s group also analyzed the potential of reovirus-mediated oncolysis for breast cancer. Direct activating mutations in the ras proto-oncogene in breast cancer are rare [45]. Breast tumor-derived cell lines were efficiently lysed by the virus, whereas normal breast cells resisted infection in vitro. Viral administration could cause tumor regression in a mammary fat pad model in SCID mice. Reovirus could also effect regression of tumors remote from the injection site, raising the possibility of systemic therapy of breast cancer by the oncolytic agent. Finally, reovirus could replicate in ex vivo surgical specimens. Overall, reovirus shows promise as a potential breast cancer therapeutic. One possible explanation for reovirusinduced oncolysis in the absence of oncogenic ras might be a ras-independent inhibition of PKR activation, which has been described for this type of cancer. Alternatively, the ras pathway might be activated by other means, such as an aberrant function of the receptor tyrosine kinase. To test reovirus as a potential therapeutic agent against lymphoid malignancies, a number of lymphoid cell lines and primary human lymphoid cell cultures, as well as normal lymphocytes and hematopoietic stem/progenitor cells, were characterized with regard to their susceptibility to reovirus infection. There was evidence of efficient reovirus infection and cell lysis in the diffuse large B-cell lymphoma cell lines and in the Burkitt lymphoma cell lines Raji and CA46, but not in Daudi, Ramos, or ST486. Moreover, when Raji and Daudi cell lines were grown subcutaneously in SCID/nonobese diabetic (NOD) mice and subsequently injected with reovirus intratumorally or i.v., significant regression was observed in the Raji-induced, but not the Daudi-induced, tumors. These data are consistent with the in vitro results. Susceptibility to reovirus infection was also detected in the majority of primary lymphoid neoplasias tested but not in the normal lymphocytes or hematopoietic stem/progenitor cells [46] Finally, the potential to be an antimetastatic cancer agent through remote-site delivery was demonstrated [47]. In particular, the ability of reovirus to replicate in murine cells to test


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the efficacy of this virus in eliminating distal or metastatic tumors in immune-competent mice was exploited. Intravenous therapy with reovirus not only inhibited metastatic tumor growth, it also led to a significant improvement in animal survival. Moreover combining i.v. reovirus treatment with immune suppression resulted in further reduction of tumor size and a considerable prolongation of survival. Combined therapy was also effective in overcoming an existing immunity to reovirus for inducing metastatic tumor regression. These results show the feasibility of i.v. reovirus therapy as a novel alternative in the treatment of metastatic cancer in humans. In summary, reoviruses have been shown to effectively destroy many different types of neoplastic cells, including those derived from brain, breast, colon, ovaries, lymphoid malignancies, and prostate. Although it was well tolerated in immune-competent and athymic mice, toxicity was demonstrated in SCID mice. In humans, reovirus either results in an asymptomatic infection or mild gastroenteritis. It can normally be isolated from the respiratory and digestive tracts, however, it is not associated with any disease state. The benign nature of this virus was also confirmed upon experimental intranasal inoculation of reovirus in adult human volunteers, which produced only mild symptoms. Therefore, the safety profile of reovirus in immune-competent humans is promising. However, its safety profile in immunosuppressed humans still has to be demonstrated. Given its selectivity for the activated Ras pathway, its effectiveness against a variety of human cancer cells in vitro and in vivo as xenografts, as well as its safety profile in humans, reovirus is an attractive candidate for oncolytic treatment. Clinical trials, which are presently being performed, will show whether the pre-clinical results can be translated to a benefit for cancer patients. REFERENCES 1. Garcia-Sastre A. Inhibition of interferon-mediated antiviral responses by influenza A viruses and other negative-strand RNA viruses. Virology 2001; 279:375–384.

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2. Egorov A, Brandt S, Sereinig S, Romanova J, Ferko B, Katinger D, Grassauer A, Alexandrova G, Katinger H, Muster T. Transfectant influenza A viruses with long deletions in the NS1 protein grow efficiently in Vero cells. J Virol 1998; 72: 6437–6441. 3. Garcia-Sastre A, Egorov A, Matassov D, Brandt S, Levy DE, Durbin JE, Palese P, Muster T. Influenza A virus lacking the NS1 gene replicates in interferon- deficient systems. Virology 1998; 252:324–330. 4. Bergmann M, Garcia-Sastre A, Carnero E, Pehamberger H, Wolff K, Palese P, Muster T. Influenza virus NS1 protein counteracts PKR-mediated inhibition of replication. J Virol 2000; 74:6203–6206. 5. Wong LH, Krauer KG, Hatzinisiriou I, Estcourt MJ, Hersey P, Tam ND, Edmondson S, Devenish RJ, Ralph SJ. Interferonresistant human melanoma cells are deficient in ISGF3 components, STAT1, STAT2, and p48-ISGF3gamma. J Biol Chem 1997; 272:28779–28785. 6. Mundschau L J, Faller DV. Oncogenic ras induces an inhibitor of double-stranded RNA-dependent eukaryotic initiation factor 2 alpha-kinase activation. J Biol Chem 1992; 267:23092–23098. 7. Richardson JC, Akkina RK. NS2 protein of influenza virus is found in purified virus and phosphorylated in infected cells. Arch Virol 1991; 116:69–80. 8. Yasuda J, Nakada S, Kato A, Toyoda T, Ishihama A. Molecular assembly of influenza virus: association of the NS2 protein with virion matrix. Virology 1993; 196:249–255. 9. Chen W, Calvo PA, Malide D, Gibbs J, Schubert U, Bacik I, Basta S, O’Neill R, Schickli J, Palese P, Henklein P, Bennink JR, Yewdell JW. A novel influenza A virus mitochondrial protein that induces cell death. Nat Med 2001; 7:1306–1312. 10. Luytjes W, Krystal M, Enami M, Pavin JD, Palese P. Amplification, expression, and packaging of foreign gene by influenza virus. Cell 1989; 59:1107–1113. 11. Parvin JD, Palese P, Honda A, Ishihama A, Krystal M. Promoter analysis of influenza virus RNA polymerase. J Virol 1989; 63:5142–5152.


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12. Garcia-Sastre A, Palese P. Genetic manipulation of negativestrand RNA virus genomes. Annu Rev Microbiol 1993; 47: 765–790. 13. Enami M, Luytjes W, Krystal M, Palese P. Introduction of sitespecific mutations into the genome of influenza virus. Proc Natl Acad Sci U S A 1990; 87:3802–3805. 14. Pleschka S, Jaskunas R, Engelhardt OG, Zurcher T, Palese P, Garcia-Sastre A. A plasmid-based reverse genetics system for influenza A virus. J Virol 1996; 70:4188–4192. 15. Neumann G, Watanabe T, Ito H, Watanabe S, Goto H, Gao P, Hughes M, Perez DR, Donis R, Hoffman E, Hobom G, Kawaoka Y. Generation of influenza A viruses entirely from cloned cDNAs. Proc Natl Acad Sci U S A 1999; 96:9345–9350. 16. Fodor E, Devenish L, Engelhardt OG, Palese P, Brownlee GG, Garcia-Sastre A. Rescue of influenza A virus from recombinant DNA. J Virol 1999; 73:9679–9682. 17. Nemeroff ME, Barabino SM, Li Y, Keller W, Krug RM. Influenza virus NS1 protein interacts with the cellular 30 kDa subunit of CPSF and inhibits 3′end formation of cellular premRNAs. Mol Cell 1998; 1:991–1000. 18. Fortes P, Beloso A, Ortin J. Influenza virus NS1 protein inhibits pre-mRNA splicing and blocks mRNA nucleocytoplasmic transport. EMBO J 1994; 13:704–712. 19. Lu Y, Qian XY, Krug RM. The influenza virus NS1 protein: a novel inhibitor of pre-mRNA splicing. Genes Dev 1994; 8: 1817–1828. 20. Li Y, Chen ZY, Wang W, Baker CC, Krug RM. The 3′-end-processing factor CPSF is required for the splicing of single-intron pre-mRNAs in vivo. RNA 2001; 7:920–931. 21. Hatada E, Saito S, Fukuda R. Mutant influenza viruses with a defective NS1 protein cannot block the activation of PKR in infected cells. J Virol 1999; 73:2425–2433. 22. Tan SL, Katze MG. Biochemical and genetic evidence for complex formation between the influenza A virus NS1 protein and the interferon-induced PKR protein kinase. J Interferon Cytokine Res 1998; 18:757–766.

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23. Lu Y, Wambach M, Katze MG, Krug RM. Binding of the influenza virus NS1 protein to double-stranded RNA inhibits the activation of the protein kinase that phosphorylates the elF-2 translation initiation factor. Virology 1995; 214:222–228. 24. Salvatore M, Basler CF, Parisien JP, Horvath CM, Bourmakina S, Zheng H, Muster T, Palese P, Garcia-Sastre A. Effects of influenza A virus NS1 protein on protein expression: the NS1 protein enhances translation and is not required for shutoff of host protein synthesis. J Virol 2002; 76:1206–1212. 25. Enami K, Sato TA, Nakada S, Enami M. Influenza virus NS1 protein stimulates translation of the M1 protein. J Virol 1994; 68:1432–1437. 26. de la Luna S, Fortes P, Beloso A, Ortin J. Influenza virus NS1 protein enhances the rate of translation initiation of viral mRNAs. J Virol 1995; 69:2427–2433. 27. Aragon T, de la Luna S, Novoa I, Carrasco L, Ortin J, Nieto A. Eukaryotic translation initiation factor 4GI is a cellular target for NS1 protein, a translational activator of influenza virus. Mol Cell Biol 2000; 20:6259–6268. 28. Goodbourn S, Didcock L, Randall RE. Interferons: cell signalling, immune modulation, antiviral response and virus countermeasures. J Gen Virol 2000; 81:2341–2364. 29. Talon J, Horvath CM, Polley R, Basler CF, Muster T, Palese P, Garcia-Sastre A. Activation of interferon regulatory factor 3 is inhibited by the influenza A virus NS1 protein. J Virol 2000; 74:7989–7996. 30. Wang X, Li M, Zheng H, Muster T, Palese P, Beg AA, GarciaSastre A. Influenza A virus NS1 protein prevents activation of NF-kappaB and induction of alpha/beta interferon. J Virol 2000; 74:11566–11573. 31. Bergmann M, Romirer I, Sachet M, Fleischhacker R, GarciaSastre A, Palese P, Wolff K, Pehamberger H, Jakesz R, Muster T. A genetically engineered influenza A virus with ras-dependent oncolytic properties. Cancer Res 2001; 61:8188–8193. 32. Stojdl DF, Lichty B, Knowles S, Marius R, Atkins H, Sonenberg N, Bell JC. Exploiting tumor-specific defects in the interferon pathway with a previously unknown oncolytic virus. Nat Med 2000; 6:821–825.


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43. Wilcox ME, Yang W, Senger D, Rewcastle NB, Morris DG, Brasher PM, Shi ZQ, Johnston RN, Nishikawa S, Lee PW, Forsyth PA. Reovirus as an oncolytic agent against experimental human malignant gliomas. J Natl Cancer Inst 2001; 93: 903–912. 44. Hirasawa K, Nishikawa SG, Norman KL, Alain T, Kossakowska A, Lee PW. Oncolytic reovirus against ovarian and colon cancer. Cancer Res 2002; 62:1696–1701. 45. Norman KL, Lee PW. Reovirus as a novel oncolytic agent. J Clin Invest 2000; 105:1035–1038. 46. Alain T, Hirasawa K, Pon KJ, Nishikawa SG, Urbanski SJ, Auer Y, Luider J, Martin A, Johnston RN, Janowska-Wieczorek A, Lee PW, Kossakowska AE. Reovirus therapy of lymphoid malignancies. Blood 2002; 100:4146–4153. 47. Hirasawa K, Nishikawa SG, Norman KL, Coffey MC, Thompson BG, Yoon CS, Waisman DM, Lee PW. Systemic reovirus therapy of metastatic cancer in immune-competent mice. Cancer Res 2003; 63:348–353.

7 Vesicular Stomatitis: an Oncolytic Virus that Exploits Tumor-Specific Defects in the Interferon Pathway REBECCA ANN C. TAYLOR, JENNIFER M. PATERSON, and JOHN C. BELL Ottawa Regional Cancer Centre Research Laboratories Ottawa, Ontario, Canada

ABSTRACT Vesicular stomatitis virus (VSV) is part of a new generation of small RNA viruses being developed as replicating cancer therapeutics. Vesicular stomatitis virus replicates in and kills a wide variety of human cancer cell lines, and is highly effective in mouse cancer models. It is exquisitely sensitive to the antiviral effects of the interferon (IFN) family of cytokines and its oncolytic activity depends on the presence of inherent de597

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fects in the IFN signaling pathway in cancer cells. Recent research has shown that IFN-inducing VSV mutants are attenuated in normal cells, but not in cancer cells. These mutants can be administered i.v. to mice at high doses, and can effect durable cures in disseminated cancer models. Other research has highlighted the potential of VSV engineered to express transgenes that could enhance the antitumor immune response, cause bystander-cell killing, or retarget VSV to receptors expressed at high levels on cancer cells. Now that several first-generation oncolytic viruses have entered into clinical trials, the lessons learned from these viruses can be applied to second-generation viruses, such as VSV, to develop more effective, safe, replicating cancer therapeutics. ONCOLYTIC VIRUSES ARE REPLICATING CANCER THERAPEUTICS One of the expectations of the genomics revolution was that an understanding of the genetic differences between normal and diseased cells would lead to rationally designed therapeutics that could target those differences and thus avoid systemic toxicity. Although targeted drugs and gene therapy have had positive results in cancer therapy, they may be limited by inefficient delivery. Oncolytic viruses can take advantage of rational drug design principles, but as in situ replicating therapeutics, they can spread to and kill target cells that might otherwise be difficult to reach. The idea of using replicating viruses to selectively kill cancer cells is not new; in fact, J. G. J. F. Sinkovics and J. C. Horvath reported the oncolytic effects of VSV in mouse cancer models was reported as early as 1969 [1]. However, the application of modern recombinant DNA technology to engineer better oncolytic viruses is new, and the field has exploded in the 10 years since the first report concerning Herpes simplex virus (HSV) in 1991 [2]. Adenoviruses were the first genetically engineered oncolytic viruses to be tested in humans [3]. Deletion of the E1B region resulted in a virus, ONYX-015, that could only replicate

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in cells with deficiencies in the p53 pathway, a characteristic shared by more than 50% of tumor cells [4]. Although this virus has proven to be very safe, its attenuation may have compromised its efficacy [5]. Since the early trials with ONYX015 and HSV, there has been a shift toward developing viruses that replicate rapidly using their own polymerase in the cytoplasm, rather than the host polymerase in the nucleus. Examples include reovirus, vaccinia, measles, polio virus, Newcastle disease virus, and VSV (reviewed in [6] and [7]. Several characteristics of VSV suggest that it may be able to fulfill the full potential of oncolytic viruses. It replicates extensively in a wide variety of human cancer cells, it is not a natural human pathogen, and it can be easily genetically manipulated and purified. THE BIOLOGY OF VSV Vesicular Stomatitis Virus has been Studied Extensively As a member of the genus Vesiculovirus of the Rhabdoviridae family, VSV is among the simplest of the RNA viruses in terms of its structure, genetics, and physiology and for this reason it is exploited as a model system for the study of viral replication and cytopathology. Vesicular stomatitis virus is an enveloped virus with a nonsegmented RNA genome of 11 kb encoding five mRNAs and give principle proteins, as well as several less well characterized internally initiated proteins. Structurally, it is divided into the ribonucleoprotein core and the viral membrane, as illustrated in Figure 1. The single-strand negative sense RNA, the N (nucleocapsid) protein, collectively with the P (phosphoprotein) and L (large) protein form the ribonucleoprotein core—a transcription unit that will synthesize, cap, and polyadenylate mRNAs in vitro. The L protein serves as the RNA-dependent RNA polymerase (RNP) but phosphorylated P is an absolute requirement for transcription [8]. The genome RNA, when tightly complexed with the N protein, is ribonuclease resistant and serves as the template for transcription [9]. The viral membrane is composed of the membrane spanning G (glycoprotein) and the M (matrix) protein, along with lipids and cholesterol derived from the host cell.

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Figure 1 Diagram of Vesicular Stomatitis Virus (VSV), illustrating virion structure (a) and genome structure (b). This virus forms a bullet-shaped particle, enveloped in a host-derived plasma membrane, containing all five viral proteins and the single-stranded negative-sense RNA genome. The L (Large) protein forms the major component of the RNA-dependent RNA polymerase, along with P (Phosphoprotein) and N (Nucelocapsid) protein, which also has a role packaging the genome. The G (Glycoprotein) forms a glycosylated trimer that binds the host receptor, phosphatidylserine, and mediates pH-dependent membrane fusion. The M (Matrix) protein has a role in virus assembly and budding, cytopathic effects, and shutoff of host-cell defenses. The virion polymerase transcribes the five mRNAs in sequential order from the 3′ end, as shown in (b). The polymerase pauses at the end of each transcript, and reinitiates with imperfect efficiency, such that genes at the 3′ end (N) are transcribed more than genes at the 5′ end (L), providing a mechanism of regulation of gene expression. The leader (le) and trailer (tr) regions are transcribed, but not translated.


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Binding of VSV to the cell surface and membrane fusion are mediated by the G protein. Not surprisingly, this viral surface protein is also the major antigenic determinant of VSV and stimulates a very strong antibody response [10]. The M protein is multifunctional in that it plays a crucial role in directing viral assembly and budding and has a number of cytopathogenic functions ascribed to it. These include inhibition of host transcription [11], disorganization of the cytoskeleton resulting in cell rounding and detachment [12], induction of apoptosis [13] and the inhibition of nucleocytoplasmic transport of mRNAs and proteins [14]. Infection with VSV begins with viral adsorption to the cell membrane by G protein binding to the ubiquitous phosphatidylserine and, possibly, other receptors. Receptormediated endocytosis and subsequent pH-dependent membrane fusion releases RNPs into the cytoplasm. The negativestrand RNA is transcribed sequentially into the five mRNAs: N, P, M, and L are translated by free cytoplasmic ribosomes, whereas G is translated on ribosomes bound to the endoplasmic reticulum, where the protein product becomes glycosylated and shuttled to the cell membrane. Viral RNA replication begins with synthesis of a full-length positive-strand copy of RNA, which serves as a template for the progeny negativestrand genomic RNA. These newly synthesized RNPs and the M protein are transported to the G protein-containing plasma membrane where viral assembly and budding is initiated [15]. Both the P and the M mRNAs encode additional proteins, the functions of which have not been fully elucidated [16,17]. An extensive understanding of the viral components of VSV and their interaction in the host cell will be invaluable for elucidating and manipulating its oncolytic properties. For example, the inhibition of mRNA nuclear export by the M protein of VSV is critical for its ability to evade the innate antiviral response and replicate in normal cells, whereas the strong antibody response induced by the G protein poses a significant barrier to in vivo viral replication during a multidose treatment regimen. Moreover, an appreciation of the life cycle of VSV is important because the relatively short replication will permit rapid viral spread, and its occurrence entirely

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within the cytoplasm ensures that VSV has no transforming ability by inadvertent incorporation into the host cell DNA. Not a Human Pathogen Vesicular Stomatitis Virus might at first appear to be an unlikely candidate for an oncolytic virus because its natural host is not human but livestock. In cattle and swine, the two main serotypes, New Jersey (NJ) and Indiana (IN), both cause a self-limiting disease clinically undistinguishable from footand-mouth disease. Vesicular stomatitis virus is endemic from northern South America to southern Mexico, where seasonal outbreaks infect roughly 10% of cattle every year, and sporadic outbreaks have been described in the southwestern United States. Although the natural life cycle of VSV is unknown, evidence suggests that insects, notably black flies and sand flies, carry the virus in endemic areas and are capable of infecting animals and, presumably, humans [10]. However, animal hosts with sustained viremia have never been found, strongly suggesting that they are dead-end hosts from which the virus does not return to its cycle in nature [11]. Under laboratory conditions, VSV cultures can be subjected to strong selective forces [9], however, extensive population studies among livestock have shown no evidence of immunological selection; VSV is genetically stable despite high levels of neutralizing antibodies among cattle populations [18]. In nonendemic areas, VSV infection in humans is rare and results in an influenza-like illness that is uniformly nonfatal [10]. These epidemiological data have important implications for the development of VSV as a therapeutic agent. First, they alleviate concern regarding the spread of VSV from the index treatment case to the population by establishing animals as dead-end hosts. Second, because VSV is a genetically stable virus in vivo, it is unlikely that VSV will mutate to a more virulent form following infection. Third, naturally occurring human VSV infection results in tolerable flu-like symptoms, and the virus is quickly and completely cleared. Moreover, because most humans are seronegative, the virus has an opportunity to replicate before neutralizing antibodies develop.


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Exquisitely Sensitive to Interferon Vesicular stomatitis virus is so well known for its interferon (IFN) sensitivity that an International Unit of IFN activity is defined by the ability to inhibit VSV replication. Interferon-␣ and -␤ are cytokines that belong to the family of Type I IFNs responsible for conferring an antiviral state in cells by the expression of IFN-stimulated genes (ISG). The IFN response results in an antiviral state consisting of cell-cycle arrest, inhibition of host translation, mRNA degradation, and apoptosis (Figure 2). Interferon-␣ and -␤ signal through Type I IFN receptors (IFNAR), which are associated with two Janus tyrosine kinases (Jak) and two signal transducer and activator of transcription molecules (STAT). The binding of Type I IFNs to their receptor results in transphosphorylation of Jaks and subsequent phosphorylation of STAT 1 and 2. The phosphorylated STATs form a heterodimer that translocates to the nucleus, where it associates with the DNA-binding protein IFN regulatory factor (IRF)-9 (previously termed p48). This heterotrimeric complex, known as ISGF3, binds to an IFN-stimulated response element to induce the transcription of more than 300 different ISGs [19]. The induction of the IFN-␣ and -␤ genes themselves is mediated by two IFN regulatory factors, IRF-3 and IRF-7, which define the first and the second wave of IFN production [20]. In the first wave following viral infection, IRF-3, which is constitutively expressed in all cell types, is activated by phosphorylation virus-activated kinases, recently reported to be members of the IKK family of kinases [21]. Interferon regulatory factor-3 translocates to the nucleus as a homodimer and binds to the IFN-␤ promoter as part of a multiprotein transcription-promoting complex called the enhanceosome that also contains nuclear factor-␬B (NF␬B), IRF-1 and ATF-2/cJun [19]. Once synthesized and secreted, IFN-␤ signals via the Type I IFN receptor to induce the synthesis of IRF-7, resulting in the second wave of the cascade. Interferon regulatory factor7 is also a transcriptional activator that turns on the synthesis of IFN-␣ and many other ISGs. Interferon-␣ also signals via the Type 1 IFN receptor, resulting in a feedback loop that is

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Figure 2 Cellular Response to Viral Infection. Infection with vesicular stomatitis virus (VSV) initiates the interferon (IFN) signaling cascade that results in a number of antiviral processes, including mRNA degradation, translational arrest, cytotoxic T-cell activity, cell-cycle arrest, and apoptosis. 1. Double-stranded RNA activates 2–5 oligoadenylate synthetase, leading to the production of RNAse L and viral mRNA degradation. 2. Protein kinase (PKR) is activated by autophosphorylation in response to dsRNA and, in turn, affects several pathways, including phosphorylation of eIF2␣ and subsequent translational arrest, activation of NF␬B and IRF-1, components of the enhancesome complex formed on the IFN-␤ gene promoter, and the transcriptional upregulation and activation of p53, the downstream effects of which include cell-cycle arrest and apoptosis. 3. Viral proteins result in the activation of the virus-activated kinase (VAK), leading to the phosphorylation of IRF-3 and its translocation to the nucleus where, along with NF␬B and several other transcription factors, it forms the enhancesome and transcriptional upregulation of IFN-␤. Interferon-␤ is synthesized and secreted from the cell where it binds to Type 1 IFN receptors on the cellular surface (itself and neighboring cells). This interaction results in the phosphorylation of signal transducer and activator of transcription molecules (STAT) 1 and 2 and, along with phosphorylated


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essential for IFN priming, a phenomenon whereby pretreatment of cells with a low dose of IFN enhances IFN production during viral infection [20]. It is also essential for protective IFN signaling from infected cells to neighboring uninfected cells. Of the many ISGs, the best-understood IFN-regulated pathways include the Mx family of proteins and the two double-stranded RNA (dsRNA)-dependent enzymes, the 2–5 oligoadenylate synthetase/RNase L system (2–5 OAS), and the protein kinase PKR. The Mx proteins belong to the dynamin family of guanosine triphosphatases. The human cytoplasmic MxA protein has been shown to inhibit viral replication at the level of transcription, as is the case with VSV [21], or at the posttranscriptional and translational levels, as seen with influenza [22] and measles [23]. The 2–5 oligoadenylate synthetases are transcriptionally induced by IFN but require dsRNA as a cofactor for activation. These enzymes polymerize adenosine triphosphate to produce 2′–5′ linked oligoadenylates whose only known function is to activate the latent ribonuclease RNase L. Activated RNase L mediates the antiviral activity through cleavage of single-stranded RNA, as demonstrated by the correlation between RNase L activation and IFN-induced inhibition of encephalomyocarditis virus [24], vaccinia virus [25], and reovirus infection [26]. The most extensively studied IFN-induced protein is PKR. Similar to 2–5 OAS, the transcription of PKR is upregulated by IFNs but the PKR protein needs to be activated by dsRNA. The PKR protein kinase is a serine-threonine kinase that undergoes autophosphorylation upon activation, which enables it to phosphorylate substrate targets. The translation initiation factor eIF2␣ is one such target, resulting in the effective shutdown of protein synthesis [27]. PKR upregulates the 䉳 IRF-9, leads to the formation of the ISGF-3 complex on the IRF-7 promoter. 6. Once synthesized, IRF-7 is phosphorylated by the VAK, resulting in its translocation to the nucleus and transcriptional pregulation of IFN-␣ and a number of other ISGs responsible for the variety of downstream effects of IFNs.

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activity of several transcription factors, including NF␬B, IRF1 [28], both components of the enhanceosome complex critical for the induction of IFN-␤. Protein kinase PKR is also found in a complex with STAT1, which dissociates upon PKR activation, allowing STAT1 to participate in the signaling cascade via the Type 1 IFN receptor [29]. In addition, PKR has been shown to regulate the activity of the tumor suppressor p53 and members of the stress-activated protein kinases, p38 MAP kinase and c-Jun NH2-terminal kinase, JNK [30]. The modulation of these varied targets by PKR confers a regulatory ability on diverse cellular processes, such as cell growth and differentiation, apoptotic, antitumor and, of course, antiviral activities. The biological importance of PKR in regulating virus infection is underscored by the existence of a multitude of viral inhibitors to PKR action, including adenovirus (inhibition of PKR activation), reovirus (sequestration of dsRNA), hepatitic C Virus (HCV) (inhibition of PKR dimerization), Herpesvirus (synthesis of PKR pseudosubstrates) and polio virus (PKR degradation) [27]. Interferons also signal through a number of alternative pathways include upregulation of caspases involved in the apoptotic cascade, cyclin-dependent kinase inhibitors, such as members of the p200 family and c-myc, exerting negative regulation of the cell cycle, and of major histocompatibility complex (MHC) Class I proteins for immune stimulation via cytotoxic T cells [19]. The relative importance of each component of the IFN signaling cascade remains to be elucidated. In mouse experiments of VSV infection, treatment with Type I IFNs, even several days after inoculation, increases survival, whereas blocking the IFN response, either with antibodies or by using IFN␣- or IFN␤-receptor knockout mice, decreases survival [31]. Similarly, mice lacking STAT1 [32] or p48/IRF-9 [33] genes are also remarkably susceptible to lethal infection with VSV. A clear role for PKR in IFN-mediated resistance to VSV has also been established by D. F. Stojdl [34]. In this study, fibroblasts derived from PKR-/- mice were shown to be more permissive to VSV infection than wild-type fibroblasts and to be deficient in IFN-mediated protection. In addition, PKR-/- mice were acutely susceptible to intranasal VSV


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infection and succumbed to an overwhelming respiratory infection, with an LD50 of less than 15 particle-forming-units (PFU) per mouse. By comparison, wild-type mice had an LD50 of 106 PFU and manifested central nervous system pathology, most notably hind limb paralysis. Moreover, pretreatment of wild-type mice with IFN-␣ or IFN-␤ completely alleviated symptoms of VSV infection, whereas pretreatment of PKR-/mice resulted in no increase in survival or alleviation of symptoms. In an earlier study by Zhou et al, [35] VSV infection of fibroblasts from mice deficient in either PKR or triply deficient in PKR, Mx1, and RNAse L was 50- to 100-fold less inhibited by IFN than in RNAseL-/- or control mice. This suggests that PKR is largely responsible for the difference in the antiviral effect of IFN observed between the control and triply deficient fibroblasts following VSV infection. This difference notwithstanding, at the highest dose of IFN, more than 103 units of inhibition were observed in the PKR-/- and triply deficient mice, providing clear evidence for the existence of alternative antiviral pathways. EXPLOITING DEFECTS IN CANCER CELLS Tumor Cells Demonstrate Defects In Interferon Signaling Interferons orchestrate a cascade of gene expression that leads to a number of fundamental changes in basic cell physiology, apart from induction of the antiviral state, are implicated in the antitumor response, including cell cycle arrest, differentiation, apoptosis, and immunomodulation. These cellular effects are the basis for their use in the treatment of neoplastic disease but, unfortunately, in the majority of cancers, IFNs have so far proven largely ineffective and patients who do respond to IFN therapy often have, at best, a short-lived remission [36]. This occurs because during tumor evolution, there is selective pressure for mutations in components of the IFN pathway, allowing cancer cells to acquire a growth and survival advantage over normal cells. Defects in IFN signaling may involve the inability to produce IFNs in response to viral

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infection, the inability to respond to IFN via the Type 1 IFNAR, or defects in specific ISGs. Inability of cancer cells to produce IFNs may occur secondary to loss of heterozygosity at IFN ␣ and ␤ loci, as was demonstrated by deletions on chromosome 9p found in a number of human gliomas [37]. Alternatively, production of IFN may be impaired by defects in components of the enhanceosome [38], whereas submaximal induction of IFN is secondary to defects in IRF-1 and IRF-7 [39]. Interferon regulatory factor-3 appears to be involved in virus-induced oncogenesis given that the E6 oncoprotein of human papillomavirus (HPV) binds to and inhibits its transcriptional activation of IFN-␤ [40]. Loss of IRF-1, a demonstrated tumor-suppressor gene, is thought to be a critical event in the development of leukemia and has also been implicated in esophageal and gastric adenocarcinomas [41]. In addition, invasive human breast carcinomas [42] and aggressive malignant melanomas [43] are significantly less likely to express IRF-1 compared with normal or less invasive tumors. By contrast, overexpression of IRF-2, which blocks transcriptional activation of IRF-1 by competitive binding, causes oncogenic transformation of NIH 3T3 cells [44] and the ratio of IRF-1/IRF-2 mRNA levels are increased in proliferating cells [41]. Although PKR appears to be involved in the activation of IRF-1, NF␬B, and ATF-2, PKR deficiency has not been demonstrated to impair virus- or dsRNA– dependent activation of IFN-␣ or IFN-␤ [45]. Tumor cells are also characterized by defects in their ability to respond to IFN signaling, including STAT phosphorylation and the formation of ISGF3. Human melanoma cells [46] and several transitional carcinoma cell lines [47] have been demonstrated to be deficient in the ISGF3 components, particularly STAT1, and the ‘suppressor of cytokine signaling’ SOCS-3, which is known to inhibit STAT1 activation, confers IFN resistance in cutaneous T-cell lymphoma [48]. In addition, the HPV oncogene E7 abrogates the antiviral effects of IFN␣ in cervical carcinoma cells by preventing the translocation of p48/IRF-9 to the nucleus [40], whereas the oncogene E6 reduces Jak-STAT tyrosine phosphorylation in human fibrosarcoma cells [49].


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Inhibition of ISGs has also been demonstrated in a number of human malignancies. Downregulation of IFN signaling is thought to be involved in prostate tumor progression because expression of 2–5 OAS and IRF-9 were found to be decreased in tumorigenic as compared with nontumorigenic prostatic hyperplasia cells and, moreover, 30% of human prostate adenocarcinoma samples exhibited downregulation of IFN-inducible genes [50]. What about the link between PKR and cancer? The role of PKR as a tumor-suppressor gene is still unclear. The expression and activity level of PKR have been shown to correlate with the degree of cellular differentiation in a variety of carcinomas, including lung, leukemia, breast, adenocarcinoma of the colon, and squamous cell carcinomas of the head and neck, but this has not been demonstrated in all cancer types [51]. In tissue culture cells, expression of either a dominant negative PKR or a PKR inhibitor, such as a variant of eIF2␣ that cannot undergo phosphorylation, leads to malignant transformation of NIH 3T3 cells [52]. In contrast, however, several studies of mice devoid of PKR protein or of PKR activity have not demonstrated increased tumorigenesis in these animals [45,52]. Mouse embryonic fibroblasts derived from mice with targeted disruption of the catalytic domain of PKR displayed normal virus- and stress-induced apoptosis and intact eIF2␣ phosphorylation, establishing the existence of a redundant pathway that can compensate for deficient PKR activity and maintain appropriate control of cell growth and apoptosis [52]. Although defective PKR alone may not be sufficient to promote unregulated cell growth, in combination with defects in other oncogenic pathways, PKR may be important for malignant transformation. The protein kinase PKR may also be linked to oncogenesis by both its upstream and downstream pathways. Upstream of PKR, Ras activation, a hallmark of malignant transformation, downregulates PKR activity through induction of an endogenous PKR inhibitor [53]. Downstream, PKR activates the tumor suppressor p53 by an NF␬B-dependent transcriptional upregulation and by phosphorylation. Defects in p53 or Ras activation are present in the vast majority of solid tumors,

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placing PKR at the center of a number of integrated and aberrant signaling pathways in cancer cells. Selective Replication In Tumor Cells With Defects In The Interferon Pathway Although tumor cells have gained a growth and survival advantage by acquiring defects in the IFN signaling pathway, they have simultaneously compromised their ability to defend themselves against certain pathogens. Because IFN is clearly essential for the defense against VSV it was hypothesized that VSV might replicate and spread more efficiently in cancer cells than in normal cells. Indeed, Several human tumor cell lines infected with VSV demonstrated earlier, had more extensive cytopathic effects, and yielded 101 to 104 more viral PFU/mL than normal human primary cell cultures [54]. Furthermore, IFN pretreatment completely protected normal primary cells and reduced viral production to less than 1,000 PFU, whereas tumor cell lines remained susceptible to VSV and continued to produce high viral titers. Moreover, in a mixed culture of leukemic cells from an Acute mylogenous Leukemin cell line and normal bone marrow cells, VSV demonstrated selective destruction of leukemic cells, even in the absence of IFN, illustrating the potential to use VSV in ex vivo bone-marrow purging. A similar study [55] also established the utility of VSV as an oncolytic agent by demonstrating efficient replication and cytolysis in a number of different human cancer cell lines with incomplete protection following IFN-␤ pretreatment. Interestingly, a second study by the same group [56] also demonstrated normal PKR activation and eIF2␣ phosphorylation in response to VSV infection in rat C6 glioblastoma cells, implying that other components of the IFN pathway and not PKR itself are responsible for the oncolytic activity of VSV in this cell line. This study also suggests that VSV kills infected tumor cells by inducing apoptosis. Several groups investigated the in vivo oncolytic of VSV in human tumor venografts in a thymic mice [54–56]. These studies demonstrated significant tumor regression following intratumoral injection of VSV with residual virus in the tumor


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tissue but virtually no virus detectable in the lung, brain, kidney, spleen, or liver 21 days after infection [55]. Similar results were seen in athymic mice implanted with c-myc or Kras–transformed BALB/3T3 cells, suggesting the potential of VSV against malignancies with a wide range of genetic lesions [56]. In terms of viral toxicity, whereas one group [56] used a fairly low dose of an VSV (2.5 ⳯ 107 PFU/mL) and observed no overt illness apparent in the treated animals during the study, another group [54] used a higher dose (108 PFU/mL) and found these immune-compromised mice began to die by day 10 of infection. In the latter study, however, mice that received IFN treatment during the infection were protected and survived symptom-free for more than 45 days. Finally, VSV is capable of reaching and replicating distal to the site of administration, and oncolytic viral replication has been demonstrated in tumors following i.v. injection and contralateral intratumoral injection [56]. As will be discussed below, results from our lab have established the in vivo efficacy of i.v.-administered VSV in a metastatic mouse model of colon cancer disseminated to the lung. Naturally Occurring Interferon-Inducing Vesicular Stomatitis Mutants Have A Wider Therapeutic Index We have shown that wild-type VSV can cure nude mice of human melanoma, although all animals eventually succumb to virus-induced mortality. These mice can, however, be completely protected from VSV by treatment with IFN, leaving tumor-killing ability intact [54]. As discussed above, VSV is exquisitely sensitive to exogenously administered IFN, but the Indiana strain of VSV itself induces very little IFN. It therefore was reasoned that a virus that could induce more IFN would retain its tumor-killing ability, yet be attenuated in normal cells. Several IFN-inducing VSV mutants have been characterized in the literature [57,58]. These mutants have substitutions in the Matrix protein that result in decreased ability of the virus to inhibit host gene expression, including IFN induction. We

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have shown that the VSV mutants AV1 and AV2 induce 20 to 50 times more IFN than the parental wild-type virus on epithelial cell lines. Furthermore, these viruses retain their tumorkilling ability against 75% to 80% of cell lines in the NCI 60 panel of human cancer cell lines. As expected, most of the cell lines in this panel have defects in their response to IFN. The mechanism by which some mutants induce more IFN than the wild-type VSV has been investigated in some detail. Expression of the wild-type M protein inhibited the transcription of transfected reporter genes [59] but mutant M proteins did not [60]. The physiological relevance of this phenomenon was confirmed by Ferran and Lucas-Lenard, who showed that the wild-type M protein also reduced expression of genes under the control of the human IFN-␤ promoter [61]. Although such studies favored a model in which M protein inhibits host transcription, other results provided evidence that the wild-type M protein actually inhibits nucleocytoplasmic trafficking, including mRNA export [14]. Further evidence has been provided to support both hypotheses (for example, Ref. 62,63), as well as another hypothesis, in which the VSV M protein inhibits STAT activation [64]. We have performed quantitative Reverse transcription (RT)-PCR to show that although AV1, AV2, and wild-type VSV Indiana induce equivalent levels of IFN-␤ mRNA in the nucleus, cytoplasmic IFN-␤ mRNA was reduced by almost 100-fold in wild-type virus-infected cells, providing further support for the nuclecytoplasmic transport hypothesis. The attenuation of IFN-inducing VSV mutants has been confirmed in animals. For example, we have shown that the LD50 for AV1 is more than four logs greater than wild-type VSV administered intranasally into Balb/C mice. Importantly, the tumor-killing ability of AV1 and AV2 is maintained invivo. In a nude mouse model of intraperitoneally injected human ovarian cancer cells, three intraperitoneal doses of AV2 can durably cure 70% of mice, whereas a single dose of the wild-type virus is lethal. Furthermore, AV1 and AV2 can effect complete cures in immunocompetent models of subcutaneous and metastatic cancer. The development of these IFN-inducing mutants represents a major advance in VSV oncolytic therapy, because all previous experiments used viruses that were


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toxic when systemically administered to animals at high doses, unless exogenous IFN was applied. These IFN-inducing mutants, however, spread poorly in normal tissue, and therefore can be administered safely at very high doses, while tumor killing remains potent. Another safety advantage of the IFNinducing viruses is that the IFN they induce also inhibits replication of the wild-type virus, so that if a revertant strain were to arise, it could not overwhelm the attenuated virus. As discussed above, the selective oncolytic ability of VSV appears to depend on tumor specific defects in the IFN pathway. Because IFN is crucial to the innate defense against all viruses, one would expect that other viruses could also selectively target tumor cells, and indeed this appears to be the case. It has been reported that reovirus [65] and some HSV mutants [66] replicate selectively in cell with an activated Ras pathway because of the Ras-mediated upregulation of a PKR inhibitor. Furthermore, an influenza virus lacking the NS1 gene, the protein product of which inhibits host gene expression in general and the IFN pathway in particular, has also been shown to have selective oncolytic properties [67]. It will be interesting to see whether other viruses can also be rendered selectively oncolytic by manipulation of their IFN-antagonizing abilities.

ENGINEERING TO IMPROVE ONCOLYTIC EFFICACY Another advantage of using VSV as an oncolytic platform is the relative ease with which it can be genetically engineered. A system has been established in which VSV can be rescued by cotransfecting plasmids encoding N, P, L, and the genome to be rescued [68]. Extra coding regions can be inserted with stability between the G and L genes. As discussed below, transgenes can be inserted that will increase toxicity to cancer cells, attenuate the virus in normal cells, induce an antitumor immune response, or provide a simple means of monitoring therapeutic progress. Furthermore, existing VSV genes can be specifically mutated, swapped, or rearranged in order [69].

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Increasing Toxicity Although VSV is a potent and rapidly cytolytic virus in vitro, multiple high doses of VSV seem to be required for durable cures, indicating that VSV is not killing all tumor cells in a single dose. Thus, it was reasoned that there may be room to increase the toxicity of VSV by engineering it to express thymidine kinase (TK) [70]. Thymidine kinase is an enzyme encoded by HSV that maintains a nucleotide pool, allowing infected cells to recycle nucleotides for DNA synthesis. It has often been used as a suicide gene in gene therapy because it converts the nontoxic prodrug Ganciclovir into a toxic metabolite and has a relatively strong bystander effect, being able to kill nearby nontransduced target cells, (reviewed in Ref. 70). G. Barber’s group showed that combined treatment with VSVTK and Ganciclovir was significantly better than wild-type VSV at inhibiting subcutaneous tumor growth in two different immunocompetent mouse models. The authors also noted that VSV-TK plus Ganciclovir was significantly better than either VSV-TK alone or Ganciclovir alone. It has been suggested that arming oncolytic viruses with suicide genes such as TK could also provide a fail-safe mechanism for stopping viral replication in an undesirable context [71]. However, because VSV is highly sensitive to IFN, we believe that administration of exogenous IFN might be a faster and more effective way to halt viral replication. Increasing Induced Antitumor Immunity Although oncolytic viruses, because they are replicating therapeutics, have a better chance of targeting all cancer cells than do chemotherapeutics, the possibility still exists that a single cell will escape and proliferate. The most effective oncolytic viruses therefore need to induce an antitumor immune response. Tumors, although they may express foreign antigens, do not appear to stimulate an effective immune response, possibly because the antigens are not presented in the context of other ‘‘danger’’ signals. Viruses, however, are very efficient at stimulating the immune system, and may be able to supply these missing danger signals to tumor cells (reviewed in Ref. 72). In-


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deed, lysates of vaccinia virus-infected tumor cells are more efficient at stimulating an antitumor immune response than lysates of uninfected tumor cells [73]; and this therapy has been applied in clinical trials [74]. Another example is replicating HSV, which has been shown in several systems to induce a longlasting protective tumor-specific immune response [75]. Vesicular stomatitis virus may also elicit this type of antitumor immune response. We have observed that five out of five immunocompetent mice cured of subcutaneous tumors for more than 7 months could not be reseeded with the same tumor cells. G. Barber’s group hypothesized that the antitumor immune component of VSV oncolysis might be increased in a virus expressing IL-4 [70]. This cytokine has been shown to play a role in tumor rejection and is known to skew the immune response toward an antibody-mediated defense [76]. In two immunocompetent mouse models, intratumorally injected recombinant VSV–IL-4 was significantly better than the wild-type virus at inhibiting subcutaneous tumor growth. Histological examination of these subcutaneous tumors revealed significant inflammatory infiltration, especially in VSV–IL4 treated animals. However, no difference in tumorspecific cytotoxic T lymphocyte activity was observed in animals treated with the wild-type versus IL-4–expressing viruses. Although VSV–IL4 may merit further investigation, viruses expressing other immunomodulatory transgenes may have greater potential. Oncolytic viruses expressing IL-2, tumor necrosis factor, B7.1, IL-10, IL-12, IFN-␥, and several others are currently under investigation [77]. Retargeting the Vesicular Stomatitis Virus Glycoprotein Vesicular stomatitis virus has the ability to enter virtually all cell types, because it uses the ubiquitous phosphatidylserine as a receptor. Whereas all published strategies for enhancing the tumor selectivity of VSV have focused on events occurring after the virus has entered the cell, research into VSV as a therapeutic against human immunodeficiency virus (HIV) has

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demonstrated that VSV is amenable to glycoprotein engineering as a means of conferring selective killing [78]. In this work, the VSV glycoprotein gene was deleted and replaced with CD4 and CXCR4, the receptors expressed on T-cells that mediate HIV entry. This novel VSV could bind to and enter only CD4Ⳮ T-cells that were infected with HIV and was able to reduce HIV titers from infected cells by up to 104-fold. Clearly, the possibility exists that VSV, like other viruses and gene therapy vectors [79], could be specifically targeted to receptors that are overexpressed on cancer cells. PROSPECTS FOR FUTURE RESEARCH The areas in which currently used chemotherapies fail are those where oncolytic viruses hold the most promise. Traditional cancer therapeutics are limited by their toxicity to normal tissue because they exploit the proliferative capacity of malignant cells and therefore target all normal rapidly proliferating cells, leading to the most common dose-limiting side effects of chemotherapy, including neutropenia and enteral toxicity. Although newer, rationally designed chemotherapeutics generally target specific defects found in particular cancer cells, they are limited by the development of a resistant population of malignant cells within the tumor. Vesicular stomatitis virus and other oncolytic agents are postulated to be superior because they target multiple defects in the IFN pathway that combine to mediate susceptibility to VSV, so the chance of complete reversion to an IFN-sensitive VSV-resistant phenotype is less likely than for other targeted therapeutics. Furthermore, oncolytic viruses can amplify themselves by more than 1,000-fold in a single tumor cell with the potential to spread to all susceptible cells. Wild-type VSV has been shown to efficiently kill a wide range of human tumor cell lines, and can effect durable cures in a variety of cancer models with several different routes of administration. Recently, research in our lab has demonstrated that IFN-inducing VSV mutants are attenuated in normal cells, yet retain their tumor-killing ability, and therefore can be safely administered i.v. at high doses.


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Certainly, future research with VSV will involve engineering recombinant viruses expressing novel transgenes to enhance the therapeutic index, but VSV is also an ideal virus with which to try more innovative tumor-specific regulatory mechanisms. DNA viruses, including adenovirus and HSV, have been extensively engineered with conditional promoters. For example, several adenoviruses were engineered with either the E1A or E4 regions under the control of tumor-specific promoters responsive to estrogen, hypoxia, telomerase, or a functional Rb pathway [80]. Because VSV transcription occurs in the cytoplasm using its own polymerase, host-specific promoters cannot be used to regulate VSV transcription. Translational and posttranslational targeting strategies could, however, be effectively exploited by an engineered VSV. For example, several translational elements, including IRES elements and 5′UTRs, have been shown to mediate enhanced translation in malignant cells [81,82], and, in addition, protein ubiquitination and degradation can be regulated in a tumorspecific manner [83]. Thus, although VSV cannot be targeted by tumor-specific promoters, posttranscriptional strategies exist that may be even more promising. The development of VSV must also be furthered at the macroscopic level, including its delivery, spread, and biodistribution in animal models and humans. Work with Greenflourescent protein-expressing VSV in our lab has shown that i.v.-delivered VSV replicates extensively throughout lung tumors at very early time points (10 to 20 hours postinfection) whereas peak replication in subcutaneous tumors may occur slightly later. More extensive studies, perhaps using other reporter genes, such as luciferase and lacZ and in vivo detection methods, such as positron emission tomography scanning, will be useful in addressing some of these issues. Moreover, it will be increasingly important to elucidate the efficacy of VSV when combined with other cancer therapeutics, particularly radiation therapy, which has been demonstrated to increase oncolysis of other viruses. Although much work still needs to be done to establish the optimal dose, schedule, and tumor type for VSV, we believe that the IFN-inducing mutants currently under investigation in our lab possess all the requisites of a

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8 Parvoviruses As Anti-Cancer Agents JEAN ROMMELAERE, NATHALIA GIESE, CELINA CZIEPLUCH, and JAN J. CORNELIS Applied Tumor Virology Program (Abteilung F0100 and Institut National de la Sante´ et de la Recherche Me´dicale U375) Deutsches Krebsforschungszentrum, Heidelberg, Germany

OUTLINE As a result of their oncotropism, oncolytic activity, and low capacity for danger signaling, some autonomous parvoviruses open new prospects to cancer therapy. Pilot Phase I clinical trials in humans using natural parvoviruses and pre-clinical studies in animals using both wild-type parvoviruses and vector derivatives transducing various cytokines, lend credit to the possible application of these agents to the fight against cancer. The oncosuppressive effects of natural and recombi627

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Rommelaere, Giese, Cziepluch, Cornelis

nant parvoviruses are reviewed, and possible mechanisms are discussed in the light of recent findings in the field of immunotherapy, which bear relevance to the development of more potent parvovirus-based anticancer agents. VIRAL LIFE CYCLE All members of the family Parvoviridae are nonenveloped nuclear-replicating single-stranded DNA viruses of only 20 nm to 25 nm in size. Members able to infect vertebrates can be placed into one of three genera. The genus Dependovirus comprises the so-called adeno-associated parvoviruses (AAV), which need assistance from some tumor viruses for their efficient replication, whereas the genera Parvovirus and Erythrovirus contain the autonomously replicating viruses, which do not require any helper viruses for productive infection. The only autonomous parvovirus known to be a human pathogen so far is the Erythrovirus B19 [1], yet further discoveries of new types cannot be excluded, as demonstrated by the recent description of a novel human skin parvovirus [2]. Despite growing evidence of a link between B19 and serious health problems (in particular the development of rheumatoid arthritis), attempts are being made to utilize the tropism of B19 toward erythropoietic progenitor cells for gene therapy [3]. This review focuses mainly on rodent viruses of the genus Parvovirus (shortly parvoviruses) such as MVM (minute virus of mice) and H-1 virus, which are for three reasons of main interest for applications in humans: (1) these agents can preferentially infect and kill a number of transformed human cells, (2) infection with H-1 virus seems to be apathogenic in adult humans, and (3) these viruses display oncosuppressive properties in vivo, for which implanted human tumors can be targets [4–7]. Relevant work performed with a number of closely related parvoviruses, such as the mouse virus MPV-1 (mouse parvovirus-1) and the rat viruses KRV (Kilham rat viruses), RPV-1 (rat parvovirus-1) and LuIII, is discussed as well. Parvovirus infection is thought to proceed as follows: The virus adsorbs on to the host cell through binding to a membraneassociated receptor that is unknown for rodent parvoviruses. In

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case of the canine parvovirus (CPV), which binds the transferrin receptor, dynein- and microtubule-dependent passage through lysosomes has been demonstrated [8,9]. Minute virus of mice was recently shown to target late endosomes and the proteasome for cytoplasmatic trafficking [10]. Once decapsidated, single-stranded DNA genomes can be converted in the nucleus into a double-stranded form. This reaction has been demonstrated to depend on the S phase-specific factor cyclin A [11], banning parvovirus replication in resting cells. Conversion creates the template for expression of genes encoding the regulatory NS1 and NS2 proteins controlled by the P4 promoter (Figure 1A). Like the conversion reaction, the activity of this strong promoter is induced in the S phase of the cell cycle, mainly owing to E2F and ATF recognition elements [12,13]. The P38 promoter, which drives the expression of the genes encoding the structural capsid proteins, requires NS1 for transactivation [14]. Conversion is also required for subsequent genome amplification through a rolling circle-like mechanism and for the production of single-stranded progeny genomes, which proceeds concomitant to their packaging into preformed capsids [15,16]. In contrast to the related AAVs, autonomous parvoviruses showed no evidence so far of DNA integration in the host genome [17]. Whereas genome amplification and single-strand DNA synthesis require NS1 functions, the initial conversion reaction only relies on cellular factors. NS1 seems to be the main cytopathic effector of autonomous parvoviruses, although in some cell lines, NS2 was shown to modulate cell killing [18–20]. The mechanism by which NS1 induces cell killing is not understood. However, NS1 is known to induce pleiotropic effects, which could well contribute to cell death because they may cause cell-cycle arrest, chromatin-nicking, and alteration of both the posttranslational modifications and localization of cellular proteins [21–26]. A number of in vitro transformed and tumor-derived cells appear to provide an internal milieu favoring parvovirus replication (discussed below). This oncotropic behavior is also reflected by the fact that several of these viruses have been isolated from tumor material [27]. First thought to be tumor

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Figure 1 Schematic representation of the genome organization of autonomous rodent parvoviruses (A) and derived recombinant viruses as described in this chapter (B). A. The viral genome (thick line) flanked by palindromic sequences at both ends is depicted on top. Messenger RNAs (thin lines) are aligned underneath, with the positions of the transcription start sites for the P4 and P38 promoters indicated by flags. The NS- and VP-coding regions in the three reading frames are indicated by boxes marked in black, gray, and white. The genome terminal hairpins and RNA introns are not to scale. B. Inserted foreign cDNA is indicated by the open box labeled ‘‘transgene.’’ The residual downstream VP sequence is not translated and varies in length depending on the transgene. The replicative and transactivating functions of the NS1 polypeptide are indicated by closed and open arrow heads, respectively.


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viruses, on the contrary, parvoviruses were soon proved able to preferentially kill human tumor cells [28]. It is therefore not surprising that trials were initiated in humans with the hope of controlling neoplastic diseases by means of these lytic viruses. OUTCOME OF PARVOVIRUS-BASED THERAPIES IN HUMANS The first case of clinical application of parvoviruses dates back to 1965, when two girls with terminal osteosarcoma were treated with H-1 virus [29]. The choice of the tumor was based on the unique osteolytic effects of H-1 virus on developing bones of young infected hamsters [30]. Prior to application of the virus, both patients had undergone intensive yet unsuccessful courses of chemo- and radiation therapy. Extensive inoperable metastases and very poor prognosis left little hope for cure, and H-1 virus was administered in an attempt to control the neoplasms. Given a single time (intramuscularly [i.m.] and intratumorally [i.t.] for the first patient, i.m. for the second one), the H-1 virus inoculum was well tolerated, yet it failed to significantly affect tumor growth and to prevent the lethal outcome of the disease after about 1 month. From our recent pre-clinical studies using MVMp in mouse tumor models, it appears that this poor therapeutic efficiency may be ascribed, at least in part, to the inoculation of too-low doses of viruses in regard to the massive volumes of the tumors to be destroyed [31,32]. Another factor limiting parvovirus efficacy might be the rapid and strong humoral antiviral response of the host, as concluded from the analysis of blood samples taken at intervals [29]. Interestingly, the aforementioned patients underwent a viremia that showed a cyclic pattern: H-1 virus particles could be detected in the blood only from day 1 to 5 and 8 to 10 postinfection. The first wave of viremia most likely reflected the initial dissemination of virions from the inoculation site through the bloodstream [1] to the liver, where particulate materials (in particular, viruses, including MVM and AAV) are cleared [33] and [2] to the host cells, the majority of which are competent for virus uptake [31]. The second wave

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of viremia was probably attributable to the release of viruses from some of the latter cells as a result of the cytotoxicity of either the virus itself or specific immune effector cells [natural killer (NK) cells, cytotoxic T lymphocytes (CTL) or antibodydependent cytotoxic cells]. Whatever the relative roles liver clearance, depletion of permissive cell reservoirs, intracellular degradation and innate or acquired immunity may have played in virus elimination, no virus could be detected in blood, tumor, liver, or kidney upon autopsy at 40 days postinfection. Furthermore, the strong neutralizing activity of circulating antibodies spoke against the usefulness of repeating the administration of the same virus over a prolonged period of time. A positive outcome of this trial lay in the absence of detectable untoward effects in virus-injected patients. Together with virus elimination, this tolerance argued for the safety of human treatment with H-1 virus, although no long-term follow-up could be done. Conclusions from this initial case study were confirmed and extended in a Phase I clinical trial conducted in the early 1990s, again using parvovirus H-1 [34]. Limitations of this study lay in the strict enrollment criteria, preventing the selection of specific malignancies, and in the application of suboptimal virus doses. All 12 recruited patients had a history of previous unsuccessful treatments and were in a terminal stage of disease, carrying skin metastases from different kinds of solid tumors. The virus was inoculated into preselected neoplastic nodules through single or repeated injection. As in the previous clinical study, H-1 virus did not induce detectable toxicity, and the maximum tolerated dose was not attained in patients who received as much as 1010 PFU of virus (approximately 1013 physical particles). This dose, however, was not sufficient to reduce the size of the metastatic foci. Nevertheless, a response to the treatment, defined as a stabilization of injected nodules according to the World Health Organization criteria, was observed in three of seven patients with mammary and in one patient with bronchial carcinoma. None of the patients with kidney leiomyosarcoma (0/1), melanoma (0/2) or pancreatic carcinoma (0/1) showed clinical improvement. All patients developed neutralizing antibodies, indicat-


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ing viral escape to the bloodstream and viremia similar to the situation observed during treatment of the osteosarcoma patients [29]. It is noteworthy that markers of virus replication and infectious virus could be detected in injected as well as noninjected lesions from some treated patients, but no correlation could so far be established between the stabilization of tumor size and the yield of recovered virus. Together with the fact that mammary tumor-derived epithelial cells showed a varying sensitivity to H-1 virus infection in in vitro studies [5,35], these data point to low-grade mammary carcinoma as a candidate target malignancy for future clinical trials. In summary, these first clinical studies showed that parvovirus application can be considered rather safe. The lack of curative effect can probably be attributed, at least in part, to the fact that the tumor load was already very high at the time of virus injection. Hence, the development of recombinant parvoviruses capable of triggering antitumor bystander responses appears to be a very promising road to follow. MOTIVATION FOR THE FURTHER DEVELOPMENT OF PARVOVIRUS-BASED THERAPEUTICS AGAINST CANCER The development of parvoviruses as therapeutics for cancer treatment is founded on experimental observations discussed in the following paragraphs and demonstration that parvovirus infections interfere with tumor establishment and growth in various experimental settings. As outlined below, a further argument in favor of parvoviruses is their relative safety, which can be traced back to a low incidence of preimmunity and lack of danger signals. Major parameters influencing the outcome of parvovirus antitumor therapy are summarized in Figure 2. Parvovirus Preimmunity is Low To date, a major obstacle to the success of gene therapy protocols using viral vectors lies in the occurrence of antiviral immune responses. Despite limitations imposed by the emer-

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Figure 2 Parameters influencing the outcome of parvoviral antitumor therapy.

gence of neutralizing antibodies, a pitfall common to all virusbased therapies, MVMp and H-1 parvoviruses have, in our opinion, an immunological ‘‘profile’’ that makes them more suitable than other viruses for anti-cancer applications. In contrast to herpes-, adeno- and adeno-associated viruses, MVMp and H-1 are not common infectious agents in humans (27, and our own observations), resulting in the absence of pre-existing immunity against the latter viruses in the great majority of the human population. This is of clear benefit, regarding both efficiency and safety. In some studies, pre-existing antibodies were described as a positive factor in that they were able to limit the dissemination of adenovirus to peripheral organs and to restrict viral expression to the tumor site [36]. Yet the lethal outcome of a recent case of adenovirusbased therapy is currently questioned as a fatal consequence of extreme activation of the complement system by a high virus dose in the context of pre-existing adenoviral immunity


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[37,38]. In contrast, the absence of pre-existing immunity against rodent parvoviruses should allow the initial inoculum of MVMp or H-1 viruses to be delivered efficiently to tumors without the risk of immediate side effects. Parvoviruses Fail to Signal Danger The immune system evolved to recognize and eliminate pathogenic invaders, including viruses, through both innate and adaptive immune reactions. Capsids and DNA of various viruses proved able to activate distinct defense cells through the recognition of Toll-like receptors (TLR) by pathogen-associated molecular patterns (PAMPs), leading to the production of endogenous danger signals that trigger local inflammation [39–41]. Furthermore, TLR-triggered signaling emerges as a link between innate and adaptive immunity in that it is essential for the maturation of dendritic cells (DC), their migration to draining lymph nodes, and the optimal antigen presentation, which enables the clonal expansion of effector lymphocytes. Results of in vivo studies involving the injection of H-1 or MVM viruses in young or adult humans (H-1), mice (MVMp), or rats (H-1) failed to show any deleterious side effect. In particular, no virus-related inflammatory histological changes could be detected in organs of autopsied animals, indicating that these viruses either failed to display relevant PAMPs or developed ways to control host antiviral immune reactions [32]. Most interestingly, the immune responses elicited by MVMp in in vivo-treated mice could be distinguished from those usually seen upon virus infection in that, on the innate side, NK cells were activated but type I interferon production was not, whereas on the adaptive side, neutralizing antibodies were produced but CTLs were not significantly induced [42]. Because the early presence of blood-derived type I IFNs and the later-generation CTLs both require DCs [43–46], these observations argue against the involvement of DCs in the process of parvovirus recognition and presentation. Knowing that antibody responses may be induced without DCs as a result of interactions between antigen-specific B cells and armed CD4ⳭT cells, we assume that activation of NK cells by

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the virus creates a milieu enabling presentation of processed virus components by major histocompatibility (MHC) class II on macrophages to naı¨ve T cells. Interestingly enough and in contrast to many other viruses, one of the major known activators of DCs—TLR9-binding immunogenic CpG motifs—are statistically underrepresented in autonomous parvoviral DNA and, when present, are located within inhibitory sequences [47]. Although no information is available at present about the interaction of MVMp or H-1 virus with DCs, our results indicate that these viruses are poor direct inducers of danger signals, which is a potential advantage with regard to the safety of parvovirus-based therapies and the expression of transgenes harbored by parvoviral vectors. It should be stated, however, that parvoviruses are cytocidal agents and may still contribute to the formation of another important class of danger signals—namely, intracellular components released as a result of cell death [48]. Yet the oncolytic character of MVMp and H-1 viruses (discussed below) raises hope of these signals being preferentially generated at or in the vicinity of tumors, which would direct DC-mediated reactions against tumor cells and account for the observed lack of side effects in animal and human studies. It should not be overlooked, however, that other parvoviruses were implicated as causative agents in inflammatory and autoimmune disorders of animals [49–51] and possibly humans [52–55]. Furthermore, MVMp and H-1 viruses can be pathogenic under specific conditions in some animal species [56]. Therefore, the apathogenic behavior of MVMp in mice and H-1 in humans cannot be taken as a precedent for the general safety of autonomous parvoviruses. In conclusion, the absence of pre-existing human immunity against H-1 and MVM viruses, the apparent inefficiency of these agents in eliciting inflammatory and cell-mediated immune reactions, together with their oncotropism and lack of evidence for integration into the host genome, place these and related parvoviruses among the safest oncolytic agents presently under consideration for anticancer applications. Parvoviruses Interfere with Tumor Development Antitumor effects of natural parvoviruses were observed under three different experimental conditions: (1) Animals in-


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fected with parvoviruses at birth were protected from spontaneous or induced cancer development in later life. (2) Parvovirus-bearing animals were refractory to tumor implantation. (3) Parvovirus treatment impeded the growth of pre-established tumors. These three categories will be discussed separately below. Prevention Of Tumor Occurrence Due To Parvovirus-Infection At Birth Soon after the discovery of parvoviruses, it was realized that life carriers were protected from the occurrence of cancer to a very significant extent, as determined through the survey of large cohorts of laboratory animals. In a pioneering work, neonatal hamsters were found to be sensitive to infection with H-1 virus, with a high incidence of dwarfed and deformed animals with mongoloid traits [30]. Later in life, these deformed animals proved to have a more than 20-fold lower incidence of spontaneous tumors than noninfected animals [57]. This observation was extended by showing that the mongoloid hamsters were also more resistant to tumor induction by adenovirus 12 or dimethylbenz anthracene [4,58]. Animals infected with H-1 virus that failed to become deformed were also protected from oncogenesis, albeit to a lesser extent. Neoplastic cell cultures prepared from the tumors of noninfected control hamsters and from the residual tumors of virus-infected mongoloid animals did not exhibit a differential sensitivity to H-1 virus, allowing no conclusion to be drawn regarding the role of viral oncolysis in the prevention of tumor appearance [4]. All animals developed virus-specific antibodies, with the highest titers found in the mongoloid hamsters. Similarly, Kilham and Margolis [59] reported that newborn hamsters infected with both the rat parvovirus KRV and Moloney leukemia virus (MoLV) did not develop tumors, whereas animals inoculated with MoLV alone did. This observation was confirmed by V. V. Bergs, who showed that the incidence of leukemia in two different strains of rats injected intraperitoneally at birth with a mixture of MoLV and KRV was approximately one-third that observed in control animals inoculated with the

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MoLV tumor virus alone [60]. As in the aforementioned experiments with hamsters, the tumor-free rats had higher KRVspecific antibody titers than the leukemic animals. It was shown in other studies that the anti-parvoviral immune response elicited in neonatally infected animals was not able to free them from the virus, which could be subsequently rescued by experimental manipulations, resulting more particularly in immunosuppression or tumor induction [61]. The protection of healthy carriers from oncogenesis may thus result from the reactivation of inapparent parvovirus infections at the site of nascent tumors, followed by oncolysis. However, this possibility remains to be proven, given that the persistence of parvovirus infection in seropositive animals protecting against tumor appearance was not demonstrated in any of the experiments outlined above. It is therefore an open question whether tumor prevention in animals inoculated at birth with parvoviruses required the reactivation of infectious viruses to kill emerging tumor cells, or resulted from the induction of a lifelong antitumor immune environment. Refractoriness of Parvovirus Carriers to Tumor Implantation The pre-infection of laboratory animals with parvoviruses was found to prevent various tumor implants from taking in these recipients. Beagle puppies that were unintentionally infected with the canine parvovirus (CPV) showed a rapid regression of transplanted venereal fibrosarcomas, in contrast to uninfected animals [62]. The related feline panleukopenia virus (FPV) was also able to prevent the transplanted fibrosarcomas from developing when the virus was inoculated concomitantly with the tumor cells but at a distant site [62]. Interestingly, FPV was inefficient as an anti-cancer agent if it was applied 3 weeks after sarcoma cell implantation, suggesting that the protective action of the virus got overwhelmed by too-large tumor burdens. Puppies that were cleared from tumors were fully protected because they did not produce neoplasias when challenged with tumor cells from the same line [62]. Similar observations were made for a mouse tumor model in which close to 90% of


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the animals that had been infected with the mouse parvovirus (MPV)-1 became refractory to the development of solid or ascitic tumors after implantation of SP2/0B myeloma cells [63]. Parvovirus Treatment Of Established Tumors A number of attempts were made at arresting the growth or inducing the regression of established experimental tumors through their direct infection with parvoviruses. These approaches involved the use of transplantable tumors that were infected either prior to (ex vivo treatment) or after (in vivo treatment) their implantation in recipient animals. In 1986, E. Guetta showed that the development of tumors from Ehrlich ascites cells intraperitoneally implanted in mice could be drastically suppressed through the simultaneous subcutaneous injection of MVM [6]. This effect was obtained with the strain MVMp, for which Ehrlich ascites cells are permissive, but not with the related strain MVMi, to which these cells are resistant, arguing for the involvement of virus-induced oncolysis in the inhibition of tumor formation. The extent of tumor suppression dropped when the inoculation of virus was delayed relative to that of neoplastic cells. This again points to the critical impact of tumor load on the overall outcome after treatment with wild-type virus. Animals that rejected tumor implants as a result of the inoculation of tumor cells and the simultaneous subcutaneous injection with MVMp were fully protected against a challenge with naı¨ve ascites cells [6]. Similar anti-neoplastic effects of parvoviruses were subsequently described in other tumor models. In mice, allogeneic P815 tumors growing as ascites were rejected more rapidly as a result of the infection of recipient animals with MVMp or MVMi, whereas the growth of S-194 solid tumors was not affected by these viruses [64]. This difference correlated with the varying susceptibility of these cells to virus infection, given that P815 cells were permissive for both MVM strains, whereas S-194 cells were not. As in the previous system, this correlation suggested that parvovirus-induced tumor suppression involved, at some point, a lytic interaction between virus and neoplastic target cells. On the other hand, the long-term protection of treated animals in the absence of

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firm evidence for persistent infection raised the possibility that this phenomenon also comprised an immune component. In keeping with this possibility, MPV-1 proved to be able to suppress grafts of allogeneic tumor cells that were not susceptible to virus infection in vitro [65]. It is worth noting that MPV-1 also accelerated the rejection of allogenic and, most surprisingly, syngeneic skin grafts [65,66], arguing for immunomodulating effects of parvovirus infections. Successful treatment of established tumors with parvoviruses was also reported for F344 rats in which tumor development from transplanted large granular lymphocytic (LGL) leukemia cells could be impeded by the later infection of recipient animals with the rat parvovirus 1 (RPV1) [56]. Furthermore the intratumoral injection of H-1 virus into large allogeneic gliomas in rats led to a remarkable regression of these lesions (K. Geletneky, personal communication). In several instances, parvovirus infections that proved efficient in suppressing tumor formation when carried out ex vivo prior to or concomitantly with the implantation of neoplastic cells failed to achieve a significant or durable protection when performed in vivo through intratumoral injection. This can be illustrated by the poor ability of MVMp to suppress MHC class I-positive immunogenic H5V hemangiosarcomas [32] or P815 mastocytomas (our unpublished results) through the in vivo treatment of tumor-bearing immunocompetent mice. MVMP had still an oncosuppressive potential in these systems because its inoculation to tumor cells prior to implantation prevented P815 cells from forming tumors and H5V cell implants from relapsing and generating metastases. Similarly, no significant antitumor effect was observed after MVM infection of mice bearing M-MSV or M-MLV–induced tumors in their footpads [64]. In another mouse model, 10 daily injections of MVMp into established tumors arising from subcutaneously implanted MHC class I-negative B78H1 melanoma cells caused tumor rejection only when the lesions were smaller than 2 mm in diameter (our unpublished results). With larger lesions (2 to 5 mm), only a transient tumor-growth arrest could be achieved, and no effect was observed when the initial tumor diameter exceeded 5 mm. These various cases exemplify the general difficulty in hitting high enough num-


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bers of cells upon in vivo administration of virus-based therapeutics, and justify further efforts to improve the efficacy of such treatments (discussed below). Tumors arising from human neoplastic or transformed cells implanted in recipient animals also proved to be targets for parvovirus-mediated oncosuppression in vivo. This was demonstrated using different models of human tumor xenogafts in nude and severe combined immune-deficient (SCID) mice. The direct injection of H-1 virus at the site of subcutaneous implantation of transformed human mammary epithelial cells (HBL100) in nude mice reduced the formation of palpable tumors by 80% [5]. Furthermore, a single i.v. injection of wildtype virus in animals bearing pre-established HBL100-cellderived tumors slowed down the growth or even induced the regression of these tumors. More recently, S. Faisst [67] reported the dose-dependent regression of human cervical carcinoma cell (HeLa)-derived tumors in SCID mice as a result of a single injection of H-1 virus in the vicinity of the neoplasms. This regression was accompanied by evidence of parvovirus replication around tumor necrotic areas. In conclusion, parvoviruses are endowed with the remarkable capacity for suppressing the development or causing the regression of certain tumors, although they cannot be considered magic bullets that are active under all circumstances. In a number of cases, the protective effect of these agents was only significant in vivo when the virus was already present at the onset of tumor development, and could be overwhelmed by increasing the tumor cell load. Therefore a race seems to exist between tumor growth and the generation of antitumor agents, whether the latter are the oncolytic viruses themselves or other defense effectors induced by infection. The occurrence of parvoviral anti-neoplastic effects in immunodeficient mice and the correlation observed in some systems between the extents of tumor suppression in vivo and tumor cell sensitivity to parvovirus infection in vitro argue for viral oncolysis as one contribution to oncosuppression. Thus, the varying sensitivity of tumor target cells to the cytotoxic activity of parvoviruses represents a first level of heterogeneity in the responsiveness of different tumors to parvovirus-based therapy. On the other

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hand, varying degrees of parvovirus-induced immune responses depending on the immunogenicity of tumors and the immune status of host organisms could account for another level of heterogeneity among tumors in their responsiveness to parvovirus treatments. Still another reason for the varying susceptibility of tumors to the suppressive effect of parvoviruses probably lies in the location of the lesions, which affects their accessibility to both viruses and defense cells and may account for the relatively high rate of success met with intraperitoneally growing tumors. One of the challenges for the future therefore lies in the identification of optimal target tumors for parvovirus-based therapies. MECHANISMS UNDERLYING THE ANTITUMOR ACTIVITY OF NATURAL PARVOVIRUSES Although parvoviruses may kill tumor cells in a direct way under in vivo conditions (viral oncolysis), the success of therapy will undoubtedly depend on at least two additional bystander effects: the immunological consequences of this tumor cell death, and the virus-induced perturbation of the immune system. These various aspects will be discussed separately in the following paragraphs. Direct Evidence of Parvovirus Oncolytic Effects in Cell Cultures Preferential Killing of (Pre) Neoplastic Cells in Culture Cytocidal processes associated with tumor regression in infected animals are likely to be mediated, at least in part, by immune effector cells and do not constitute proof that the virus has a direct oncolytic activity. Therefore, in vitro cell cultures were used to determine whether parvoviruses could kill (pre) neoplastic cells in preference to the parental normal cells. Indeed, it was repeatedly observed that various normal human and rodent cells were more resistant to wild-type H-1 or MVMp infection than in vitro transformed derivatives or tumor-derived


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cells from the same tissue origin [68–75]. This holds true for cells of both mesenchymal and epithelial origins. Cultures of human tumor cells are more particularly sensitive to H-1 virus infection, albeit to various extents [5,69,75,76]. A striking example of the oncolytic effect of H-1 virus in vitro is illustrated in Figure 3. Several human leukemic cell lines could be killed

Figure 3 Hypersensitivity of a human squamous cell carcinoma cell line (c, d) to the cytopathic effects of wild-type parvovirus H-1, in comparison with normal human keatinocytes (a, c). a, c: mocktreated cultures; b, d: H1-virus infected cultures.

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very efficiently by this virus [77–80], in keeping with the lymphotropism of the closely related KRV virus in its natural host, the rat [56]. Most of these studies were conducted with cell lines that had been established in vitro and may therefore have drifted from their original physiological condition. It should be stated, however, that short-term cultures of human mammary carcinoma [35], hepatoma [81], and glioma (K. Geletneky, personal communication) cells also proved to be preferential targets for the lytic activity of H-1 virus. In the systems analyzed so far, the greater susceptibility of neoplastic or transformed cells to parvovirus infection could not be ascribed to a more efficient virus uptake and correlated with an enhancement of viral DNA replication or gene expression [73,74,82]. A parallel could be drawn between the greater parvovirus-induced killing of transformed versus nontransformed human fibroblasts and the presence of a larger fraction of cells positive for viral gene expression in the former cultures [83,84]. In some cells, parvoviruses induce a typical apoptotic type of death. For example, human promonocytic tumor cells (U937) infected with H-1 virus were killed very efficiently through apoptosis, as monitored by the appearance of apoptotic bodies and the cleavage of poly(ADP-ribose)polymerase (PARP) [80]. Interestingly, variant cell clones surviving H-1 virus infection were also refractory to tumor necrosis factor (TNF)-␣–mediated killing, suggesting that the parvovirus and TNF-␣ use at least partially overlapping signaling pathways to induce cell death. Similarly, rat glioma (C6) cells from infected cultures and cerebellum cells from infected rats were reported to be killed by H-1 virus through an apoptotic process [85]. Apoptotic death of primitive hemopoietic progenitor cells was also observed in the bone marrow of MVMi-infected mice [86]. On the other hand, HeLa cells that are also very susceptible to H-1 virus-induced death showed characteristics of both apoptosis and necrosis, depending on the conditions used [87]. In MVMp-infected rat fibroblasts, cell killing could not be attributed to apoptosis [88]. The mode of cell death is of importance when interactions with the immune system in infected organisms are considered (discussed below).


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Viral Proteins Involved in Cytotoxicity When the parvovirus gene coding for the nonstructural (NS) proteins was placed under control of an inducible promoter and stably introduced by transfection in SV40-transformed human fibroblasts, its expression correlated with a reduced number of cells able to form visible colonies [18]. Further site-directed mutagenesis studies led to the identification of the NS1 protein as a major determinant of parvovirus-induced cell disturbances [89–91]. The small parvoviral nonstructural proteins (NS2) may modulate the NS1 cytotoxic activity in a cell-dependent fashion [19]. Interestingly, when plasmids containing an inducible NS1 gene were expressed in normal rat fibroblasts or in transformed derivatives thereof, only the survival of the latter cells was impaired, suggesting that transformation sensitizes host cells to NS-induced killing [92]. The cytopathic function of NS1 is likely to be controlled by phosphorylation because distinct point mutations abrogating the proper phosphorylation of the viral polypeptid lead to the up or down modulation of its toxic activity in permissive cells [93]. It remains to be determined whether and how other viral proteins cooperate with NS1 to account for the overall cytotoxicity of parvovirus infections. The mechanisms by which parvoviruses induce the death of permissive host cells are not yet fully understood even under in vitro conditions. This is a complex phenomenon involving both subversion of cellular defense processes and cell intoxication (L. Daeffler, personal communication). As stated above, the viral NS proteins are endowed with both cytostatic and cytotoxic properties, leading cells to undergo growth arrest, morphological alterations, and loss of adherence [93]. These phenotypic changes may be traced back to one or another of the multiple molecular disturbances induced by NS proteins in target cells [26], including the formation of specific NS–cellular polypeptide complexes (25, and references therein). In various systems, these alterations can culminate in cell lysis, in which the capsid proteins may be involved (our unpublished observations).

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Indirect Evidence of Parvovirus Oncolytic Effects in Animal Models The parvoviral oncolytic effects observed in cell cultures raise hopes of a similar activity being exerted against tumors under in vivo conditions. Yet evidence of parvoviral oncolysis in whole organisms is mostly indirect. The expression of H-1 virus-cytotoxic NS proteins was detected in the necrotic zones of HeLa cell xenografts infected in vivo [67]. Furthermore, distinct necrotic foci were visible along MVM injection routes on histological sections of in vivo treated mouse melanoma implants (N. Giese, unpublished observations). Because some of these foci showed no infiltration with host neutrophils, monocytes, or lymphocytes, at least part of tumor necrosis can be assumed to be caused by the direct cytotoxic activity of the virus. This cannot be formally proven because defense cells were present in other necrotic areas of the tumor. The simultaneous occurrence of virus replication and leukocyte infiltration in regressing tumors is consistent with virus-induced oncolysis because this process is expected to be accompanied by a stimulation of local immune reactions, as discussed above. This, however, prevents a separate evaluation of the relative contributions of viral oncolysis and immune cytotoxicity through histological examination of regressing tumors. The same holds also for immunodeficient models given that innate defense mechanisms (and, in some models, antibody production) have to be taken into account. Indeed, A. Haag showed that NK cells were activated and infiltrated H-1 virus-infected HeLa xenografts in nude mice, raising the possibility that these cells may mediate, at least in part, the virus-induced suppression of tumor formation [94]. The occurrence of parvoviral oncolysis in vivo is also supported by the correlation generally observed between the sensitivity of target cells to virus killing under in vitro culture conditions, and the responsiveness of corresponding tumors to virus therapy, as determined after ex vivo or in vivo infection. Thus, the MVMp-sensitive Ehrlich ascites and P815 cells constitute tumor models that were efficiently inhibited by the parvovirus, whereas tumors derived from cells that were more resistant to MVMp either required higher virus doses to be suppressed


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(H5V) or were refractory to the virus treatment (B78H1) (31,32, and unpublished results). Similarly, Ehrlich ascites tumors could be suppressed by MVMp but not by the related strain MVMi, paralleling the sensitivity of these cells to the former virus and their resistance to the latter [6]. It should be stated, however, that the sensitivity of a cell line to parvovirus infection correlates with its greater capacity for viral gene expression (see above). Therefore, it cannot be ruled out that under in vivo conditions, the virus-induced cellular disturbances do not progress up to the stage of cell death but result in phenotypic changes that stimulate innate cytotoxic reactions against (infected) neoplastic cells, leading to the cross presentation of tumor antigens by DC and the generation of antitumor CTL. Whether initiated by viral oncolysis or virus-activated innate killer cells, this scenario would account for the long-term protection of virus-treated animals against tumor-cell challenges in the absence of detectable viral imprints [6]. Tumor Cell Targets for Parvovirus Infection From a therapeutic point of view, it would be useful to know whether specific oncogenes or tumor suppressor genes are involved in the sensitization of neoplastic cells to parvovirus attack because it would give clues to which tumor types are most appropriate for parvovirus-based treatments. On the one hand, it was shown that expression of a number of oncogene products, including MYC, SRC, RAS, and SV40 large T antigen, correlated with a greater susceptibility of rat fibroblast transformants to MVMp-induced killing, whereas the bovine papilloma virus transforming proteins were ineffective in this respect [73]. On the other hand, H-1 virus-resistant subclones derived from the H-1–sensitive human erythroleukemic cell line K562 were found to express wild-type p53, whereas this protein could not be detected by current methods in the original cell line [78]. Similarly, rat fibroblasts in which endogenous p53 was functionally inactivated by means of a dominant negative mutant thereof became more susceptible to H-1 virus infection and resultant killing compared with the parental cells expressing active p53 [78]. Furthermore, long-term cultures of Li-Fraumeni skin fibroblasts that lost their residual

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wild-type p53 allele proved to be more sensitive to H-1 virusinduced killing than earlier cell passages that still expressed functional p53 (our unpublished results). As a whole, these data indicate that the permissiveness of cells for parvovirus infection can be up- and down-modulated as a result of the expression of oncogenes and tumor suppressor genes, respectively. The mechanisms by which these genes affect the outcome of parvovirus infection are currently under investigation. One of the levels at which this modulation takes place was assigned to the activation of the viral early promoter P4 through specific signaling pathways [95]. An interesting parallel can be drawn between these data from autonomous parvoviruses and a recent report showing that AAV-2, a helper-dependent member of the Parvoviridae family, selectively killed human tumor cells lacking functional p53 through the induction of apoptosis. In contrast, cells with intact p53 survived the infection and became arrested in the G2 phase of the mitotic cycle [96]. These effects required very high multiplicities of infection with AAV (around 2.5 ⳯ 104 ⳮ5 ⳯ 105 particles per cell) and were apparently attributable to the incoming viral DNA. It was concluded from this work that AAV DNA, which is single-stranded, with hairpin structures at both ends, was sensed as DNA damage and elicited signals leading to death or growth arrest, depending on the p53 status of the host cell. Interestingly, the hairpin structures alone were able to trigger, at least in part, the damage response. It is noteworthy that the conditions under which AAV and autonomous parvoviruses caused cell death in a p53-dependent fashion were totally different. Indeed, the killing activity of autonomous parvoviruses was achieved using 50- to 200-fold lower multiplicity of infection (at which AAV had no effect) and required active virus replication and gene expression (in contrast to the involvement of input virus genomes in AAV toxicity) [20,80,97]. Because the cytopathogenicity of autonomous parvoviruses does not always correlate with the accumulation of viral DNA [72,74] and can result from the sole expression of NS proteins [18,92], H-1 virus and AAV appear to trigger cell death through different mechanisms. It should be stated, however, that the genomes of autonomous and


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helper-dependent parvoviruses share structural features, including terminal hairpins, which raises the possibility that at a higher multiplicity of infection, autonomous parvoviruses may provide death signals similar to those of AAVs. Most interestingly, the injection of high amounts of AAV virions (the genomes of which retained the hairpin ends) prevented the establishment of subcutaneous tumors, suppressed the growth of established tumors, or even caused their regression in various mouse models, according to the p53 status of the neoplastic cells grafted [96]. These observations give strong support to the development of drugs that mimic the DNA damage signals provided by parvoviral genomes. Indeed, one may expect that, like parvoviral DNA, these drugs will have an anti-cancer potential through their ability to kill cells devoid of functional p53 (which is the case of most human tumor cells) while sparing normal cells (with intact p53). Contribution of the Immune System to Tumor Clearance In Vivo Stimulation of Tumor Immunity The manner in which tumor cells die after parvovirus infection is not only of academic interest but constitutes an important factor determining the susceptibility of tumor cell to macrophages and DC-mediated processing, which is decisive for the induction of acquired immunity [48,98]. Irrespective of the mechanism involved, parvovirus infections appear to stimulate cells to release distress signals such as heat shock proteins [99], which are known to generate a ‘‘danger’’ environment favorable to the activation of the host immune response [100,101]. Therefore, the interaction of parvoviruses with tumors may contribute not only to the destruction of a fraction of the neoplastic cells but also to the stimulation of antitumor immune reactions. This possibility is supported by recent in vitro cross-presentation experiments showing that H-1 virus infection and ensuing killing of human melanoma cells led to DC loading with tumor antigens, whereas mock-treated melanoma cells were ineffective in this respect (M. Mo¨hler, personal communication).

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Parvoviruses as Immune Trouble Makers Treatments with MVMp and H-1 virus, including repeated injection regimens, were not associated with any detectable deleterious side effects in mouse and rat models used to demonstrate oncosuppression, nor in the human Phase I clinical trials conducted to assess tolerance (discussed above; Refs. 29,31,32,34; and K. Geletneky, personal communication). Yet pathological signs can be induced by other parvoviral infections and may shed light on at least some facets of the tumor-suppressing activity of these agents. In particular, certain parvoviruses have been implicated as causative agents in inflammatory and autoimmune diseases, including endothelialitis and rheumatoid arthritis (human B19), vasculitis, glomerulonephritis, polyarthritis and anti-DNA immunity (aleutian disease virus [ADV]), enteritis and myocarditis (CPV), and diabetes (KRV) (49–55,102,103). In some experimental settings, a strain-dependent mortality caused by intestinal and renal hemorrhages was described for neonatal mice infected with MVMi (a parvovirus with a high degree of homology to MVMp), whereas MVMp was apathogenic [64,104,105]. Infection of endothelial cells, presence of circulating antibodies, and formation of immune complexes are thought to play a major role in these pathologies. These observations raise the intriguing possibility that some aspects of parvovirus oncosuppression may be traced back to a virus-induced state of immune hyperactivity for which tumors would be preferential targets. The inter-twinning of parvovirus-mediated oncosuppression and immunomodulation can be exemplified by the effects of the lymphocytotropic MPV-1. This virus was found to potentiate rejection not only of tumor allografts but also of allogeneic and—most surprisingly—syngeneic skin grafts [63,65,66]. These reactions did not result from virus infection of the cellular or vascular components of the various grafts and were mediated by T cells. In this system, the parvovirus appears to be devoid of a direct oncolytic activity and to act by exerting immunomodulatory effects, including the disruption of peripheral tolerance and development of autoimmune responses. The immune cell targets and mode of action of MPV-1 remain to be determined. Similarly, the destruction of pancreatic ␤ cells that is responsi-


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ble for the induction of autoimmune diabetes by KRV in DR-BB rats did not appear to result from direct viral cytopathic effects, but correlated with immunological changes (induction of specific TH1-type cytokines and CD4Ⳮ cells), which may disrupt the immune balance and lead to the generation of autoreactive T lymphocytes [49,103]. In keeping with these observations, infections of rats with KRV were recently reported to trigger the release of the TH1-type cytokine IFN-␥, but not that of the TH2type cytokine interleukin (IL)-4 [106]. Besides the involvement of TH1 cytokines in the activation of autoimmune cells [107], there is more and more evidence to suggest that TH1–type responses generate a physiological milieu detrimental to oncogenesis. For instance, the antimetastatic effect of the chemical adjuvant cyclophosphamide has been ascribed to its ability to generate a TH1 cell response [108]. Furthermore, successful rejection of tumors using various immunotherapeutic approaches was shown to be accompanied with autoimmune reactions, as exemplified by skin depigmentation due to melanocyte destruction in the case of melanoma treatment in humans and mice (109,110). Therefore, conditions promoting autoimmunity appear to potentiate tumor rejection, arguing for the possibility that the competence of parvoviruses for inducing such conditions may well play an important role in the anti-neoplastic activity of these agents. A direct targeting of immune cells is observed after infection with several rodent parvoviruses that have lymphocytotropic properties [56] and therefore may hit the appropriate cells to induce changes in the immune environment. It cannot be ruled out that this scenario also applies to a so-called fibrotropic parvovirus such as MVMp because this agent was reported to infect mesenteric lymph nodes in mice [105]. Indeed, we found in our pre-clinical studies that besides neoplastic lesions, lymphoid organs were a major site of MVMp mRNA accumulation in virus-infected tumor-bearing mice [32]. Target cells for MVMp transcription in lymph nodes and spleen could be assigned to a minute subpopulation of lymphocytes rather than metastasizing tumor cells. This extra-tumoral MVMp gene expression in lymphoid tissues remains to be evaluated for its impact on tumor growth. Interestingly, a progres-

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sive disappearance of activated or memory CD8Ⳮ CD44Ⳮ CD26Lⳮ lymphocytes (N. Giese, unpublished results) was observed, which may contribute to the poor induction of virusspecific CTLs in MVMp-infected C57Bl6 mice [42]. Although MVMp gene expression proved to be restricted in various in vitro cell cultures of lymphoid origin [111], aforementioned observations suggest that immunomodulating effects of this virus still need to be considered. Together, these data also indicate that advantage may be taken of the unique lymphotropism of parvoviruses to deliver appropriate transgenes to lymphoid tissues through parvoviral vectors in immune gene therapy protocols (discussed below). PRE-CLINICAL STUDIES USING RECOMBINANT PARVOVIRUSES A most effective antitumor protection was achieved when parvoviruses were inoculated to the animals prior to the appearance of neoplasms (in particular, at birth) or to the tumor cells prior to their implantation into recipient hosts. In contrast, variable results were obtained when parvoviruses were administered to animals harboring established tumors, which may be ascribed at least in part to excessive tumor burdens. To overcome this restraint, efforts are being made to increase efficiency of parvoviruses through the inclusion of therapeutic transgenes. Construction of Recombinant Parvovirus-Based Vectors The design, production, and purification of recombinant autonomous parvoviruses have recently been reviewed [112,113] and are not discussed in detail here. It is sufficient to say that MVM and H-1 virus-derived recombinant parvoviruses designed so far for cancer therapy purposes are so-called capsid-replacement vectors, in which the P4 and P38 promoters and the NS genes from the parental virus are kept, while part or all of the capsid (VP) genes are replaced by a therapeutic transgene, as illustrated in Figure 1B [76,114–116]. These vectors are ex-


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pected to be endowed with the oncotropic and oncolytic properties of the wild-type viruses because they retain the cis- and trans-acting elements thought to be responsible for these features. Upon cell infection, the viral regulatory protein NS-1 is expressed from the genuine P4 promoter, leading to the amplification of the vector genomes and the potent transactivation of the P38 promoter. The resulting transgene expression proved to be very efficient but transient in vitro as well as in vivo, and to depend on cell oncogenic transformation [94,114], which seems especially suitable for the production of toxic principles in the context of cancer gene therapy application. The transience of transgene expression was ascribed to the cytopathic effects of the vectors, although the recombinants were found to be less toxic for some cells than the corresponding parental viruses in single-infection experiments, pointing to a possible contribution of newly synthesized capsid (proteins) to parvovirusinduced cell disturbances (unpublished results). Limitations of parvovirus-based vectors lie in the limited size of the transgenes that they can accommodate (less than 1800 bp in the aforementioned constructs) and the present difficulties in producing high-titer recombinant virus stocks. Furthermore, presently available vectors can only achieve one-hit infections because they are unable to yield progeny particles attributable to their defect in VP genes. The main features of recombinant and wild-type viruses are compared in Table 1. Improved Antitumor Capacity of Parvoviral Vectors Harboring Immunomodulating Transgenes The ultimate goal of cancer immunotherapy is to break down tolerance to tumor-associated antigens (TAAs). There is clear evidence to suggest that CTLs are major effector cells that can attack and kill tumor cells in vivo through the recognition of TAAs presented by MHC class I molecules on the neoplastic cell surface. The capture and presentation of TAAs by DCs is central to the induction of effective antitumor CTL responses. This process is dictated by the initial death of some tumor cells to promote the uptake of antigens by DCs, and by the local release of cytokines, chemokines, and heat shock proteins to

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Table 1 Properties of Natural Parvoviruses and Derived Vectors Virus Properties Stability Preparation Infectious particles/106 cells Maximum size of DNA insert DNA integration Anti-virus immune responses: Humoral Cellular Pre-existing immunity in man Safety in humans

Competence for progeny virus production Preferential binding to tumor cells Oncolysis

Wild-type

Vector(1)

Refs

Cotransfection 2⫺10⫻106

135 112, 113 113

1.8 kb

115, 116

High Infection ⬎ 109

No Evidence

Strong

17

NR

Weak

NR No or low

42, 56, 106 42 2

No adverse reaction reported Yes

NR

29, 34

No

115, 116

No

No

Yes

Yes

69, 72, 73 80

(1)

Only for the vectors described in this contribution. NR ⫽ not reported.

induce DC maturation. Innate immune cells, including NK cells, macrophages, and several types of leukocytes, are thought to play an important role in this initiation of the tumor rejection process [48,117,118]. These were the grounds for supplying parvoviruses with transgenes encoding various immunoregulatory molecules. Parvoviral vectors transducing distinct co-stimulatory molecules or cytokines and chemokines were shown to constitute valuable antitumor therapeutics in various tumor models, as summarized in Table 2. These recombinants reduce tumor growth and prolong the survival of the animals by enhancing the immunogenicity of neoplastic cells or recruiting and acti-

Nude Nude Syng Syng Syng Syng Nude Syng

HeLa human carcinoma HeLa human carcinoma K1735 mouse melanoma H5V mouse endothelioma B78/H1 mouse melanoma

Ex vivo Ex vivo Ex vivo In vivo Ex vivo In vivo Ex vivo In vivo

Protocol H-1 H-1 MVMp MVMp MVMp MVMp H-1 MVMi

Virus IL-2 MCP-1 IL-2 IP-10 MCP-3 MCP-3 MCP-3 B7.1

Transgene Yes Yes NR No Yes Yes NR NR

Wild-type Yes Yes Yes Yes Yes Yes Yes Yes

94 94 123 32 122 122 120 119

⬎ ⬃ ⬎ ⬎ ⬎

Ref

Recombinant/wt

Antitumor Effect Recombinant

Syng ⫽ syngeneic; NR ⫽ not reported; No ⫽ no antitumor effect was recorded; ⬎ ⫽ antitumor activity of recombinant greater than that of corresponding wild-type virus; ⬃ ⫽ antitumor activity of recombinant and wild-type viruses were similar.

HeLa human carcinoma EL4 mouse thymoma

Mice

Tumor models

Table 2 Anti-Tumor Effects of Recombinant Parvoviruses Transducing Costimulatory Factors or Cytokines/Chemokines

Parvoviruses As Anti-Cancer Agents 655

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vating immune effector cells. Thus, the treatment of mice bearing EL4 thymomas with a single dose of recombinant MVMi expressing the co-stimulatory molecule B7.1 elicited a protective immune response generating tumor-specific CTL memory cells [119]. Furthermore, MVMp or H-1 virus-based vectors transducing the genes encoding human interleukin (IL)-2, monocyte chemotactic protein 3 (MCP-3), or interferon (IFN)-␥–inducible protein 10 (IP-10) proved to have a significant anti-neoplastic activity in various animal tumor models in which their wild-type counterparts were inefficient (31,32,94,120,121, and unpublished results). The ability of these vectors to support a cytokine or chemokine production was demonstrated in treated animals and obviously overtook the defectiveness and reduced toxicity of the recombinants to endow them with a globally enhanced oncosuppressive capacity. In nude mice, parvovirus-mediated MCP-3 and IL-2 expression caused an intratumoral infiltration and activation of NK cells and macrophages that was associated with increased neoplastic cell killing and reduced growth of human carcinoma cell xenografts [94,120]. In immunocompetent animals, MCP-3-transducing MVMp fully suppressed the formation of neoplasias from ex vivo-infected B78H1 melanoma cells, and drastically reduced the growth of in vivo-treated established tumors [122]. Regressing or stabilized tumors were found to become infiltrated with T lymphocytes and NK cells in which the death program was activated, as revealed by positive transcription signals for IFN-␥, IL-2, Fas L, granzymes, and perforin. In another mouse melanoma model (K1735), ex vivo infection with MVMp and IL-2 was found to prevent tumors from appearing in about 70% of implanted animals under conditions in which the wild-type virus only delayed the onset of tumor growth [123]. Interestingly, tumor-free animals became resistant to a later challenge with live melanoma cells, indicating that the recombinant parvovirus elicited a longterm antitumor protection. Promising results were also obtained using parvoviral vectors to express the chemokine IP10, which binds to the CXCR3 receptor present on activated T lymphocytes, NK cells, and vascular cells. The development of syngeneic hemangiosarcomas in immunocompetent mice


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Figure 4 Suppression of primary tumor relapse and metastases formation (open arrow heads) through infection of hemangiosarcoma-bearing mice with recombinant MVMp expressing the chemokine IP-10. (From Ref. 32.)

could be efficiently suppressed through multiple intratumoral injections of IP-10–transducing MVMp recombinants [32]. As illustrated in Figure 4, besides the recurrence of primary tumors, the formation of multiple metastases in the liver, spleen, uterine tubes, peritoneal cavity, and ovaries was drastically reduced in animals treated with MVMp and IP-10. In summary, these data show that parvovirus vectors are efficient transducers of cytokines and chemokines. Therefore, they deserve to be assessed for applications in the immune gene therapy of cancer. PERSPECTIVES Besides inclusion of immunomodulating transgenes, as outlined above, further attempts are currently being made to improve the potential of autonomous parvoviruses for cancer therapy through virus engineering. Possible strategies are the insertion of cytotoxic transgenes, alteration of the pattern of virus-driven gene expression through modification of the P4 promoter, or modulation of NS1-mediated toxicity through

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site-directed mutagenesis. In this context, the possible application of parvoviruses in vaccination strategies is elaborated. Transduction of Cytotoxic Transgenes Besides their direct contribution to the reduction of the tumor load, suicide genes encoding conditional toxins may also stimulate antitumor immunity by promoting the uptake of dying tumor cells by DCs and the presentation of tumor antigens to T cells [98]. A recombinant MVMp expressing the conditionally toxic Herpes simplex virus thymidine kinase gene, proved able, in vitro, to cause efficient killing of a number of tumor cell types in the presence of the prodrug ganciclovir, while having no or little effect on normal proliferating cells [83]. Similar attempts were recently made using H-1 virus-based vectors that transduced and expressed the chicken anemia virus product Apoptin [124]. As a result of the ability of this polypeptide to induce death specifically in transformed cells [125], the H-1/Apoptin recombinants were capable of killing in vitro a greater proportion of human tumor cells than transgene-free viruses, without becoming toxic for nontransformed cells. In vivo experiments are awaited to assess the oncosuppressive potential of this class of recombinant parvoviruses. Vaccination A number of clinical trials lend credit to the use of DNA vectors for vaccination purposes [126]. The suitability of recombinant autonomous parvoviruses to achieve immunization was recently demonstrated by successfully protecting mice against Borrelia burgdorferi through intranasal or i.v. administration of a MVMi-based vector expressing the bacterial outer surface protein A (OspA) [127]. Treated mice developed high-titer antiOspA–specific antibodies that provided sustained protection from live spirochete challenge over the lifetime of the animals. By analogy, parvovirus vectors expressing tumor-associated antigens deserve to be considered as potential vaccines to elicit antitumor immunity, given their aforementioned capacity for preferentially transducing both neoplastic and lymphoid tissues. In addition, recombinant parvoviruses harboring immunomodulating transgenes might be used to facili-


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tate the recruitment, maturation, or functioning of effector cells participating in the antitumor immune response. Besides their transduction ability, parvoviruses are endowed with cytotoxic properties that promote not only the death of tumor cells but also the release of cellular danger signals such as heat shock proteins [99]. This represents a potential advantage regarding the induction of antitumor immunity, given the capacity of tumor cell lysates and, in particular, heat shock proteins for promoting tumor antigen presentation by DCs [98,117]. Parvovirus-mediated vaccination may be carried out through direct administration of the recombinant viruses in vivo, or by means of adoptive protocols in which the vectors are inoculated to tumor or immune cells in vitro. These developments are still in their infancy, but are supported by a recent attempt to suppress B78H1 mouse melanoma tumors in immunocompetent animals using wild-type MVMp and a vector derivative expressing the chemokine MCP-3 [122]. The ex vivo infection of B78H1 cells with MVMp/ and MCP-3 (but not MVMp) did not only prevent these cells from forming tumor upon implantation in recipient mice, but protected more than half of treated animals from naı¨ve tumor cell challenge over their lifetime. This system exemplifies tumors against which the wild-type parvovirus is poorly protective (correlating with a restriction on virus-driven gene expression in a large fraction of the cells), unless it is supplemented with a transgene that has an immunostimulating bystander effect. Altogether, these data suggest that the use of parvoviral vectors for vaccination purposes deserves to be further explored. Targeting Specific Tumors Through P4 Promoter Modifications The host cell range of autonomous parvoviruses can be altered by modifying the pivotal P4 promoter. This was initially demonstrated by substituting the human immunodeficiency virus (HIV) TAT protein-response (tar) element for the proximal region of the P4 promoter of parvovirus MVMi [112]. Infectious MVMi viruses harboring this substitution could be produced in a cell line constitutively expressing the HIV TAT transactivator and proved to depend on TAT for their multiplication and cyto-

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toxic effects. Although this study was aimed at killing HIVinfected cells by means of modified parvoviruses, a similar strategy may conceivably be used to target specific tumors with these agents. Indeed, tumors of a certain type may be distinguished from other tissues by patterns of oncogene and tumorsuppressor gene alterations that result in the activation of a signaling pathway involving a specific transcription factor. Advantage may be taken of this situation to design parvoviruses that depend on such a transcription factor for their replication and can be used to specifically destroy the tumor cells in which it is activated. This situation can be exemplified by human colon tumors, which are characterized by the frequent deregulation of the wnt signaling pathway [128], resulting in the sustained induction of promoters that contain binding sites for the heterodimeric Tcf/␤-catenin transcription factor [129]. This prompted us to produce hybrid H-1/MVMp viruses in the genome of which Tcf consensus binding motifs were substituted for distinct sites of the parvoviral P4 promoter [130]. These substitutions proved to make virus replication Tcf dependent, resulting in the induction of cytopathic effects in colon cell lines with high Tcf activity but not in cells that have inactive wnt signaling pathways. This is proof of principle that parvoviruses can be rendered specific for certain tumor cells through P4 promoter engineering, although the oncotropism and anti-neoplastic efficiency of viruses modified in this way remain to be assessed in vivo. Modulation of Parvovirus Cytotoxicity Through Site-Directed Mutagenesis Recent developments showed that phosphorylation events driven by protein kinases involved in the regulation of cell growth, differentiation, and transformation are essential to tune the MVM NS1 protein for induction of toxic effects in host cells. Using site-directed mutagenesis techniques to alter the phosphorylation pattern of the NS1 polypeptide, mutant MVMp viruses were generated that displayed increased or reduced toxic potentials (our unpublished observations). This gives hope of producing MVMp mutant viruses or vectors that are endowed with an enhanced oncolytic activity or a greater


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capacity for transgene expression compared with their wildtype equivalents. CONCLUSION Ongoing clinical trials, with modified adenoviruses, in particular, gave compelling evidence to suggest that virus therapy deserves to be considered among novel nonconventional approaches to cancer treatment [131]. This is especially true for tumor types against which surgical and radio- or chemotherapeutical interventions have only limited or transient efficacy and metastatic stages of cancers. In the same way the use of antimitotics is restrained by their nonspecific toxicity, a number of viruses endowed with anti-neoplastic potential can have undesirable side effects, even if they are devoid of intrinsic pathogenic activity. This can be exemplified by the life-threatening inflammatory reactions triggered by some adenoviral treatments [38]. In this respect, the rodent autonomous parvoviruses considered in this review are distinguishable in that they do not elicit overt immune reactions in animal models, even after repeated injections, and are not associated with known diseases in humans or adverse reactions in treated patients. This safety results, at least in part, from the fact that these viruses have a restricted host cell range, in spite of their ability to enter most cells in infected organisms. Thus, few of the infected cells support parvovirus replication and expression, and still fewer are capable of progeny virus production, which limits the effective virus targets to distinct tissues including in particular some tumors (hence the quotation of these agents are oncolytic). In addition, the development of a neutralizing antibody response to incoming virions certainly contributes to the containment of parvovirus infections. Yet these advantages of parvoviruses regarding safety can also represent limitations with respect to their efficiency in tumor suppression. Indeed, pre-clinical studies have shown that the protective effect of parvoviruses against cancer is significant but can often be overtaken by too-large tumor burdens. Attempts are therefore being made to improve the anti-

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neoplastic potential of parvoviruses by optimizing their oncolytic activity and taking advantage of their preferential expression in tumors and lymphoid tissues. Besides the various strategies outlined in previous sections, recent findings that still await anti-cancer applications are worth mentioning. On the one hand, parvovirus pseudotyping is feasible [132], which should increase the efficiency of multiple virus infections by minimizing the neutralization of a given inoculum by the antibodies raised against a previously administered virus batch. On the other hand, the cell-surfacetargeting specificity of members of the Parvoviridae family can be altered through capsid modifications that prevent the viruses from binding to their genuine ubiquitously expressed receptors and redirect them to distinct new cellular receptors [133]. As stated above, parvoviruses naturally possess oncotropic properties that manifest themselves at the intracellular level. Targeting of the neoplastic cell surface through capsid modifications would constitute an additional safeguard to ensure the tumor specificity of parvoviruses and, even more importantly, should increase the efficiency of parvovirus-based treatments by preventing a large fraction of the inoculated viruses from getting lost as a result of their dead-end uptake by normal tissues [31]. Besides virus engineering to improve oncosuppressive capacity, efforts are certainly worth being made to identify tumors that are most susceptible to parvovirus infection, and to combine parvoviruses with other conventional or nonconventional therapies. Particular consideration may be given to the application of parvoviruses as postoperative treatment or as a complement to immunomodulating drugs that bring neoplastic cells into contact with T cells in a lymphoid tissue environment favorable to the induction of anti-tumor immunity [134]. Recombinant parvoviruses may allow combining the viral and immune therapeutic principles in the form of a single agent. ACKNOWLEDGMENTS Relevant work in the authors’ laboratory was supported by grants from the European Union (Programme ‘‘Quality of Life and Management of Living Resources’’).


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9 Newcastle Disease Virus Oncolysate in the Management of Stage III Malignant Melanoma

WILLIAM A. CASSEL, DOUGLAS R. MURRAY, and ZBIGNIEW L. OLKOWSKI† Emory University School of Medicine Atlanta, Georgia

INTRODUCTION Awareness of tumor regression during viral infection in humans dates back to 1912, and the first virus-induced tumor lysis in a laboratory animal was observed with vaccinia virus in 1922. In clinical trials, the West Nile arbovirus was the first †

deceased 677

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Cassel, Murray, Olkowski

to show beneficial effects. It soon became evident that some tumor-destroying viruses had a predilection for neural tissues. Unfortunately, several treated patients developed encephalitis, and by 1970 interest in direct action by oncolytic viruses had essentially run its course, although the effectiveness of mumps virus, even against brain tumors, was reported in 1978. The subject is reviewed by H. E. Webb and C. E. G. Smith [1], and more recently by J. Nemunaitis [2]. Evidence that virally lysed tumors had immunizing properties was presented by G. R. Sharpless et al in 1950 [3], and H. Koprowski et al in 1957 [4]. Finally, viral oncolysates per se´ were employed to immunize laboratory animals, as described by J. Lindenmann and P. A. Klein in 1957 [5]. A virus budding from the cell membrane was an essential feature in the process. The role of the virus was elucidated by the fact that, in animals made immunologically tolerant to the virus, the oncolysates were ineffective in immunization [6,7,8]. The evidence therefore suggests that the virus acts as a helper antigen in assisting the immune system to recognize the poorly antigenic tumor cells. Application of oncolysates to humans was introduced by J. G. Sinkovics et al [9] and W. A. Cassel et al [10] in patients with sarcomas and malignant melanoma. For further orientation on viral oncolysates, the reader is referred to an excellent review by F. C. Austin and C. W. Boone [11]. RATIONALE Newcastle Disease virus (NDV) employed in our studies was acquired from the American Cyanamid Company, through the courtesy of Dr. Robert Love. The virus had extensive passage in Ehrlich ascites tumor cells in vitro and in vivo and was capable of curing mice bearing the Ehrlich ascites tumor that was allowed to progress to 41% of its potential development [12]. When cured animals were challenged with a dose of 2 ⳯ 107 tumor cells, most animals showed a solid immunity to the tumor [13]. The virus also was active against a human adenocarcinoma carried in the hamster cheekpouch, and human cervical cancer cells (HeLa). It would not multiply in the adult

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brains of six animal species [12], suggesting that NDV was safe for human application. A patient with uterine cervical cancer received a heavy dose of the virus injected into the tumor. Extensive sloughing occurred, with cessation of bleeding, shrinkage of involved lymph nodes, and considerable subjective improvement in the patient. Several years later, T. C. Merigan [14] observed this strain of NDV to be the best endogenous interferon inducer of all agents examined in humans, following intravenous administration, and no neuropathogenicity was encountered. Another cytokine induced by the virus is tumor necrosis factor, as demonstrated by R. M. Lorence et al. [15]. We considered the particulate nature of the lysate to be an asset in stimulating an immune response, as suggested by the studies of G. J. V. Nossal [16], A. L. Notkins et al [17], and D. M. Weir [18]. V. Schirrmacher et al [19], however, employing a non-lytic strain of NDV, found intact, infected cells were preferred for immunization. In our study, infectious virus was maintained in the oncolysate, for the purpose of providing a maximal impact on the patient’s immune system, and possibly to destroy directly any tumor cells remaining after surgery. All evidence indicated the virus would not be harmful to patients. A nullifying effect by antibody to the virus, developing from repeated oncolysate application, appeared minimal. J. Lindenmann and P. A. Klein [20] noted that mice immunized to influenza virus, then administered an oncolysate prepared with the same virus, were protected from challenge by the tumor employed in the lysate. A. Horak et al [21] found that in the NDV-oncolysate system, antiviral immunity induced in humans does not interfere with the development of antimelanoma immune cell responses. The presence of antibody might actually play a role in oncolysis, should the patient’s tumor cells become infected by the virus in the oncolysate and succumb to complement, NK cells, or macrophage-mediated lysis [1]. The wide spectrum of human tumor cells susceptible to infection by NDV suggested that oncolysates probably could be prepared for application in a variety of malignancies. Considering the above information, and the long-existing awareness of the antigenic nature of malignant melanoma,

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this malignancy was selected for study. We focused on Stage III (AJCC) cases: patients with regional lymph node metastases that were palpable and required therapeutic dissection. In summary, some reasons for favoring NDV as a lytic agent include: (1) The virus has not shown neuropathogenicity in humans. (2) It induces lymphokines. (3) It shows a wide range of infectivity for tumor cells. (4) It has a high neuraminidase activity [12], which could be involved in uncovering concealed antigenic sites on the tumor cell surface. (5) The virus has a stable genome, reducing the likelihood of it mutating to a harmful variant. PROCEDURES The methods employed in our studies are presented in depth elsewhere [10,22]. Oncolysates were prepared from two existing malignant melanoma cell lines and 21 cell lines established from the ongoing patients. Highly concentrated oncolysate was administered subcutaneously on the anterior thigh as a 2.5mL dose, consisting of a systematically rotated composition of autogenous and allogeneic cell lines, with three different cell lines per dose. An additional dose of 0.2 mL was injected intracutaneously on the forearm. The oncolysates were shown to be devoid of viable tumor cells. Patients were entered into the study as they presented and were confirmed as Stage III (AJCC) cases of malignant melanoma, requiring a therapeutic lymph node dissection. We introduced the practice of continuing immunization for a period of years. Treatment began 4 weeks after surgery. Oncolysate then was administered weekly for 4 weeks, followed by a 2-week schedule until week 52, at which time the interval was increased to 6 weeks. After 10 years, the patients went to a 3-month schedule. Those treated included 81 on-study, Stage III (AJCC) patients, and 80 patients with widely disseminated disease who were treated as a desperate measure. Over 11,000 doses of oncolysate were administered without any significant adverse effect, thus attesting to the relative safety of the oncolysate and its live virus component.


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CLINICAL FINDINGS With approval of the Emory University Clinical Trials Committee, the first patient was treated in 1971, and our first Phase II study reports appeared in 1977 [10,22]. A 10-year follow-up report was presented in 1992 [23]. The earliest recurrence of disease in a patient was seen after 36 weeks of treatment. At 10 years, 63% of the patients remained free of detectable disease. Currently, surviving patients have been under study for 20 to 28 years. Thirty-six (71%) of patients who survived 10 years remained free of malignant melanoma for the next 10 years, resulting in 44% of the patients remaining clinically free from disease at 20 years (Table1). Of the 15 patients lost between 10 and 20 years, six died from malignant melanoma. Each of the six patients had followed faithfully his treatment schedule up to the time of recurrent disease. The other nine patients were clinically free of malignant melanoma when they died from other causes. Although these nine patients cannot be included in the survival data, if some of them had survived to 20 years, the tumor-free survival figure would have risen. We are not aware of any other 20-year hard data on the survival of a group of Stage III (AJCC) cases. DISCUSSION We compared our survival findings in this Phase II study with those in seven independent reports concurrent with our patient accrual times [23]. These historical controls included 832 patients, and survival figures in the different studies ranged from zero to 15% at 10 years following therapeutic dissections. More recent reports describe 33% survival rates at 10 years [24,25], but 20% and 24% of the patients had elective lymph node dissections. According to D. L. Morton et al [26], there is a highly significant improved survival in patients receiving elective lymphadenectomy versus those requiring therapeutic dissections. To compare therapeutic dissections with a mixed group is tenuous. Arguably, there appears to be a consensus that the natural history of malignant melanoma has not

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changed in recent decades [27]. Historical data, therefore, should be considered acceptable for a Phase II study. Furthermore, in accord with regulations codified by the U.S. Food and Drug Administration [(21 C.F.R. 314. 111(a) (5) (ii) (a) (4)], in a disease with high risk and predictable mortality, the results of the use of a treatment procedure may be compared quantitatively to prior historical experience in the natural history of the disease. Aside from overall survival, two subgroups were noted in this study. Malignant melanoma showing regional lymph node disease of the head and neck is particularly serious. As pointed out by D. F. Roses [28], such involvement is almost a certain indication of systemic disease. We observed improved survival of head and neck cases in our treated patient group [29]. Because of time limits imposed by other reports, 29 months after surgery necessarily was taken as the time for comparisons. At this point, 71% of our patients evidenced disease-free survival, in contrast to 3% to 25% to at other institutions (Dr. Robert M. Byers, personal communication), and D. F. Roses et al [28]. The second group that drew our attention was patients with brain metastases. Surgical specimens from all six patients in this category showed striking inflammatory infiltration (lymphocytes, plasma cells) into the brain metastases [30], even though the immune reaction thus induced failed to eradicate the brain tumors. Any cellular immune response in a cerebral metastasis, particularly in malignant melanoma, is a rarity. Our uniform findings are statistically significant, and indicate an immune response induced by NDV oncolysate. Three of these patients died within 3 years after brain surgery, two from malignant melanoma and one from complications relating to surgery. The other three patients remained free of malignant melanoma relapse for 17 years, at which point two died from causes other than malignant melanoma, and the remaining patient continues to be free of detectable disease. These certainly are extraordinary survival times. Postsurgical life expectancy in patients with cerebral metastases usually is 2 to 7 months, with an occasional extension to 20 months [31,32] or, rarely, longer. The longest postoperative survival report in the English literature may be 14 years [33].


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Evidence of favorable clinical progress in the patients prompted us to perform various immunologic tests, beginning in the early phase of this study, particularly to assess cellular responses. Marked increases in lymphocyte cytotoxicity against autogenous and allogeneic target malignant melanoma cells were observed in all treated patients [10]. Support for a critical role by activated CD-8 T-lymphocytes in the eradication of malignant melanoma came from a study by Z. L. Olkowski [34], employing human malignant melanoma transplants in nude mice. T-lymphocytes from five patients, stimulated by recombinant interleukin-2, were incubated with a human melanoma cell line (M40) for several weeks. This treatment resulted in increased lymphocyte cytotoxic activity when tested against each patient’s melanoma cell line, as determined by a Cr51 release assay. Injection of the activated T-lymphocytes into nude mice bearing melanoma M40 nodules resulted in selective accumulation of the technetium 99m-labeled T-lymphocytes in the malignant melanoma nodules of the mice, providing evidence for a role of CD-8 cells in the eradication of malignant melanoma. More recently, F. M. Batliwalla et al [35] observed a marked oligoclonality of CD-8 T-lymphocytes in our patients. Cursory examination of our 20-year data (Table 1) might suggest that because almost half the surviving patients initially had a single diseased lymph node, we were dealing with a low-risk group. If so, one must explain why 56% of the patients we lost to malignant melanoma in the control group of this study also had only a solitary diseased lymph node. Furthermore, among the patients not on study, but treated for humanitarian reasons, three had failed surgery and chemotherapy, and were regarded as hopeless cases. One patient had multiple nodules of the head and neck, with metastases to the chest wall. The other two patients had 17 and 32 diseased lymph nodes. These individuals remain free of detectable disease at 29, 21, and 20 years respectively, following surgery and oncolysate treatment. Several staging systems exist for malignant melanoma, the primary purpose of which is to predict survival, and hopefully act as a guide in deciding on treatment procedure. Based

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Table 1 Clinical Data on Stage III (AJCC) Melanoma Patients Who Survived Disease Free Location of

Primary level/ thickness

Gender/ age

primary lesion

1 2 3 4 5 6 7 8 9 10 11 12 13

F/18 M/26 F/30 M/27 F/36 F/29 M/22 M/37 M/60 M/54 M/38 F/22 M/43

Scapula Shoulder Shoulder Interscapular Thigh Calf Scapula Unknown Scapula Subpateller Chest Scapula Chest

III/1.3 mm IV/1.5 mm IV/2.5 mm III/1.8 mm III/1.1 mm III/2.0 mm IV/2.1 mm Unknown Unknown II/1.0mm III/1.5 mm IV/5.5 mm IV/2.5 mm

14

F/41

Scapula

II/0.7 mm

15 16 17 18

F/39 M/36 M/32 F/52

Unknown Shoulder Subscapular Wrist

Unknown Unknown III/1.7 mm IV/2.6 mm

19 20 21

M/29 F/21 F/27

22 23 24 25 26 27 28

F/45 F/32 M/54 F/49 M/29 F/30 M/35

Unknown Gluteal fold Calf Shoulder Interscapular Knee Ear Upper arm Shoulder Calf Thigh

Unknown IV/5.0 mm III/1.1 mm II/2.3 mm Unknown V/5.0 mm IV/1.7mm IV/3.8 mm III/0.5 mm III/Unknown IV/1.7 mm

29 30 31 32 33 34 35 36

F/25 F/70 M/37 M/35 M/28 M/58 M/45 M/43

Axilla Interscapular Chest Upper arm Shoulder Lumbar Elbow Forearm

Unknown III/2.5 mm III/1.1 mm III/0.9 mm IV/1.7 mm IV/1.9 mm V/6.0 mm III/1.2 mm

Patient

Diseased lymph nodes

DF survival* (years)

4 (axilla) 1 (axilla) 1 (axilla)** 3 (axilla) 1 (groin) 1 (groin) 1 (axilla)** 2 (axilla) 2 (axilla) 1 (groin) 3 (axilla)** 1 (axilla)** 1 (axilla) 2 (in transit) 2 (axilla)** 2 (in transit) 2 (neck) 1 (axilla) 3 (axilla) 1 (axilla) 7 (in transit) 15 (axilla) 1 (groin) 2 (groin)** 0 4 (axilla) 2 (groin)** 1 (neck) 1 (axilla)** 6 (axilla)** 1 (inguinal) 3 (groin) Plus 8-cm mass 4 (axilla)** 1 (axilla) 3 (axilla) 1 (axilla) 1 (axilla) 5 (axilla) 1 (axilla)** 2 (axilla)

28 27 26 26 26 25 25 25 24 24 24 24 24 24 24 23 23 23 23 22 22 21 21 21 21 21 20 20 20 20 20 20 20 20 20 20

* Disease-free survival: Figures rounded off to the nearest year. ** Palpable lymph nodes occurring concomitantly with the primary skin lesion.


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on empirical clinical observations, such systems neglect a major part of the picture, namely, the variance in virulence of the invading tumor. Historically, the six clinical variables given in Table 1 are those most frequently seen in the literature. Other criteria exist, and as the list lengthens practical application becomes increasingly unmanageable. A current report [36] addresses the consideration of 13 variables. It is difficult to imagine doing a randomized, stratified study and finding enough patients to fill all categories. Whereas large numbers of diseased lymph nodes would portend for a poor prognosis, this is not always the case. Conversely, the presence of a solitary, palpable lymph node can lead to serious consequences. The need to complement clinical observations with scientific, laboratory methods is evident. Routine information on chromosome aberrations, oncogene amplification, tumor invasiveness in animal models and tissue cultures, gene expression profiling, and measures relating to the host’s immune reactions to the tumor could help in prognostication. Admittedly, these are sophisticated methodologies, but until a scientific base is coupled with clinical empiricism, prognosis will not be as precise as is claimed by staging systems currently in use. Methods for measuring the status of the patient’s immune system have long been available. Some of the immune reactions are not tumor inhibiting, but can be tumor enhancing instead. For a full evaluation of the host–tumor relationship, a combination of immunity status, clinical criteria, and tumor virulence is required. Although this is not beyond possibility, it is not available or routinely practiced, currently. CONCLUSION In the past five years there has been an outpouring of approximately 700 publications dealing with a vaccine or other forms of adjunctive immunotherapy for the management of malignant melanoma. Innovative approaches have included heat shock proteins, anti-idiotypic antibodies, hybrid cells, bacteria or viruses as gene vectors, oncolytic viruses, peptides, epitopes, gangliosides, dendritic cells, liposome encapsulated

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agents, cytokines, macrophage-stimulating factor, various forms of modified tumor cells, DNA vaccines, antisense oligonucleotides, and gene therapy, to mention some of the evolving methods. We believe NDV oncolysate has provided benefits for malignant melanoma Stage III (AJCC) patients, and that it should remain in place for the management of the most rapidly increasing malignancy worldwide.

ACKNOWLEDGMENTS Supported by the General Assembly of the Georgia State Legislature and the Goldhirsch Foundation. This report is dedicated to the memory of Zbigniew L. Olkowski, M.D., Sc.D.

REFERENCES 1. Webb HE, Smith CEG. Viruses in the treatment of cancer Lancet 1970; 1:1206–1209. 2. Nemunaitis J. Live viruses in cancer treatment Oncology 2002; 16:1483–1492. 3. Sharpless GR, Davies MC, Cox HR. Antagonistic action of certain neurotropic viruses toward a lymphoid tumor in chickens with resulting immunity Proc Soc Exp Biol Med 1950; 78: 270–275. 4. Koprowski H, Love R, Koprowska I. Enhancement of susceptibility to viruses in neoplastic tissues Tex Rep Biol Med 1957; 15:559–576. 5. Lindenmann J, Klein PA. Viral oncolysis: Increased immunogenicity of host cell antigens associated with influenza virus J Exp Med 1967; 126:93–108. 6. Svet-Moldavsky GJ, Hamburg VP. An approach to the immunological treatment of tumors by artificial hetrogenization. In: Harris JC, Ed. Specific Tumor Antigens (UICC Monograph Series, vol 2). Copenhegen: Munksgaard, 1967:323–327.


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7. Kobayashi H, Kodama T, Gotha E. Xenogenization of tumor cells Hokkaido Univ Med Libr Ser 1977; 9:1–24. 8. Boone CW, Paranjpe M, Orme T, Gillette R. Virus-augmented tumor transplantation antigens: Evidence for a helper antigen mechanism Int J Cancer 1974; 13:543–551. 9. Sinkovics JG, Gonzales F, Campos LT, Kay HD, Shirato E, Gyorkey F. Immunology of human sarcomas Abstracts of the Annual Meeting of the American Society of Microbiology 1974:206. 10. Cassel WA, Murray DR, Torbin AH, Olkowski ZL, Moore ME. Viral oncolysate in the management of malignant melanoma. I. Preparation of the oncolysate and measurement of immunologic responses Cancer 1977; 40:672–679. 11. Austin FC, Boone CW. Virus augmentation of the antigenicity of cell extracts Adv Cancer Res 1979; 30:301–345. 12. Cassel WA, Garrett RE. Newcastle disease virus as an antineoplastic agent Cancer 1965; 18:863–868. 13. Cassel WA, Garrett RE. Tumor immunity after viral oncolysis J Bacteriol 1966; 92:792. 14. Merigan TC, De Clereq E, Finkelstein MS, Clever L, Walker S, Waddell DJ. Clinical studies employing interferon inducers in man and animals Ann NY Acad Sci 1970; 173:746. 15. Lorence RM, Rood PA, Kelly KW. Newcastle disease virus as an antineoplastic agent: Induction of tumor necrosis factor and augmentation of its cytotoxicity J Natl Cancer Inst 1988; 80: 1305. 16. Nossal GJV. The mechanism of action of antigens Australas Ann Med 1965; 14:321. 17. Notkins AL, Mergenhagen SE, Rizzo AA, Scheele C, Waldman TA. Elevated gamma-globulin and increased antibody production in mice infected with lactic dehyrrogenase virus J Exp Med 1966; 123:349–364. 18. Weir DM. The immunological consequences of cell death Lancet 1967; 2:1071–1073. 19. Schirrmacher V, Ahlert T, Heicappell R, Appelhaus B, Hoegen P. Successful application of non-oncogenic viruses for antimetastatic cancer immunotherapy Cancer Rev 1986; 5:19–49.

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20. Lindenmann J, Klein PA. Immunological aspects of viral oncolysis Recent Results Cancer Res 1967; 9:1–84. 21. Horak A, Horvath J, Sinkovics JG, Pendleton S, Pritchard M. Antiviral and antimelanoma immune reactions in patients actively immunized with melanoma-NDV oncolysates, St. Joseph’s Cancer Institute and University of South Florida Melanoma Conference, 1998, Tampa, FL. 22. Murray DR, Cassel WA, Torbin AH, Olkowski ZL, Moore ME. Viral oncolysate in the management of malignant melanoma. II. Clinical studies Cancer 1977; 40:680–686. 23. Cassel WA, Murray DR. A ten-year follow-up of stage II malignant melanoma patients treated postsurgically with Newcastle disease virus oncolysate Med Oncol 1992; 9:169–171. 24. Callery C, Cochran AJ, Roe DL, Rees W, Nathanson SD, Benedetti JK, Elashoff RM, Morton DL. Factors prognostic for survival in patients with malignant melanoma spread to regional lymph nodes Ann Surg 1982; 196:69–75. 25. Bevilacqua RG, Coit DG, Rogatko A, Younes RN, Brennan MF. Auxillary dissection in melanoma. Prognostic variables in nodepositive patients Ann Surg 1990; 212:125–131. 26. Morton DL, Wanek L, Nizze JA, Elashoff RM, Wong JH. Improved long-term survival after lymphadenectomy of melanoma metastatic to regional nodes Ann Surg 1991; 214:491–499. 27. Morton DL, Foshag LJ, Hoon DSB, Nizze JA, Wanek LA, Chang C, Davtyan DG. Prolongation of survival in metastatic melanoma after active specific immunotherapy with a new polyvalent melanoma vaccine Ann Surg 1992; 215:463–482. 28. Roses DF, Harris MN, Grunberger I. Selective surgical management of cutaneous melanoma of the head and neck Ann Surg 1980; 192:629–632. 29. Cassel WA, Murray DR. Viral oncolysate in the treatment of regional metastases of melanoma. In: Larson DL, Ballantyne AJ, Guillamondegui OM, Eds. Cancer in the Neck. New York: Macmillan Publishing Company, 1986:235–242. 30. Cassel WA, Weidenheim KM, Campbell WG, Murray DR. Inflammatory mononuclear cell infiltrates in cerebral metastases


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during concurrent therapy with viral oncolysate Cancer 1986; 57:1302–1312. 31. Madajewicz S, Karakousis C, West CR, Caracandas J, Avellanosa AM. Malignant melanoma brain metastases. Review of Roswell Park Memorial Institute experience Cancer 1984; 53: 2550–2552. 32. Balch CM, Milton GW, Shaw HM, Soong S. Cutaneous Melanoma. Philadelphia: JB Lippincott, 1985. 33. McCann WP, Weir BKA, Elvidge AR. Long-term survival after removal of metastatic malignant melanoma of the brain J Neurosurg 1968; 28:483–487. 34. Olkowski ZL. The role of human 99mTC labeled cytotoxic lymphocytes in radioimmunodetection and potential radioimmunotherapy of malignant melanoma Immunoconjugates Radiopharmaceuticals 1991; 4:55. 35. Batliwalla FM, Bateman BA, Serrano D, Murray DR, Macphail S, Maino VC, Ansel JC, Gregersen PK, Armstrong C. A 15year follow-up of AJCC stage III malignant melanoma patients treated with Newcastle disease virus (NDV) oncolysate and determination of alterations in the CD8 T cell repertoire Mol Med 1998; 4:783–794. 36. Sprakel B, Stenschke F, Unnewehr M, Ladas A, Senninger N. Prognosis of malignant melanoma following dissection of regional lymph node metastases Der Chirurg 2003; 74:55–60.

10 Vaccinia Viral Lysates in Immunotherapy Of Melanoma PETER HERSEY Oncology & Immunology Unit Newcastle, NSW, Australia, [email protected]

ABSTRACT Melanoma continues to be difficult to treat once it has spread from its primary site in the skin. There is much evidence that immune responses against the tumor play an important role in control of the disease. Experimental evidence suggested that viral lysates of tumor cells may be effective vaccines for treatment of tumors. In view of this, we developed a vaccine from vaccinia viral lysates of a single-cultured melanoma line and tested its effectiveness in treatment of American Joint Committee on Cancer (AJCC) Stage lIB and III melanoma in 691

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a series of Phase II studies and a randomized control trial. We verified the immunogenicity of the vaccine and its safety in patients with melanoma. The Phase II studies showed impressive gains in survival compared with historical controls. The Phase III study was confounded by much longer survival of all patients in the study, which meant that the number of events was relatively low and the trial was consequently underpowered to detect the relatively small differences seen between treated and control groups. There was an improvement in the hazard of dying from melanoma of 20% but the confidence limits included 1, indicating the result may have been attributable to chance. Median survivals of control and treated groups were 88 and 151 months, respectively. There was an approximate 10% and 20% improvement in survival at 5 and 10 years, respectively, but the best P value was 0.068. The apparent benefit from this treatment may therefore have been attributable to chance but, if true, the results from the trial are superior to those from other randomized vaccine trials. Treatment was not associated with any significant side effects. Approaches to improve treatment results include co-treatment with agents that may sensitize melanoma to apoptosis and control of regulatory T cells in patients with melanoma. INTRODUCTION Patients with thick primary melanoma or regional lymph node (LN) metastases are known to be at high risk of disease recurrence and death. Previously published estimates of survival over a 5-year period approximate 63% to 67% in patients with primary melanoma 4 mm or greater in thickness (AJCC Stage IIB) and 46% to 69% in those with regional LN metastases (AJCC Stage III disease) [1–3]. Median survivals for patients with Stage IIB and III disease in three recent trials were 34 [4], 41.3 [5], and 72 months [6]. A number of different adjuvant therapies given after surgery have not been shown to reduce the risk of recurrence or death in such patients. These include chemotherapy with Dimethyl, triazero, imidazole carboxamide (DTIC) with or without immunotherapy with bacillus Calmette-Guerin [7] and recombinant interferon-␣2a (IFN␣2a) given at relatively low doses (3 million units subcutaneously three times a week) for 3 years [8,9]. Trials of IFN-␣2b

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at higher doses conducted by the Eastern Cooperative Oncology Group (ECOG) in the United States have given inconclusive results, with one trial (ECOG 1684) showing clear benefit of relapse-free (RFS) and overall survival (OS) [4], whereas a subsequent trial (ECOG 1690) showed improved RFS but no improvement in OS [6]. The most recent trial (ECOG 1694) showed benefit in terms of RFS and OS in comparison with immunotherapy with a ganglioside GM2/keyhole limport hemocyanin (GM-2/KLH) vaccine. An untreated control group was not included in the latter study.[10]. Following the disappointing results from adjuvant therapy trials of nonspecific immunotherapy with agents such as Bacillus Calmette Gue´rin (BCG) and Corynebacterium parvum [11], much interest was generated in specific immunotherapy using autologous or allogeneic melanoma cells, and particularly in the use of viral lysates. The basis for using an immunological approach in therapy was the frequent occurrence of regression of primary melanoma [12] associated with lymphocytic infiltration into the tumor [13,14] and many in vitro studies showing antibody and T-cell responses to melanoma [15,16]. The use of viral lysates as a melanoma vaccine was well founded by prior studies in animal tumor models, where it was shown that viral infection of cancer cells increased their immunogenicity [17,18]. Augmentation of immunity required that the tumor cells be infected with the virus, and separate administration of virus and tumor cells was not effective. H. Fujiwara [19] and Y. Shimizu [20] demonstrated that vaccinia virus generated T cell help against the hapten, trinitrophenyl and against syngeneic murine tumors. VACCINIA VIRUS IN IMMUNOTHERAPY OF MELANOMA Vaccinia virus is a member of the poxviruses with a nucleoprotein core and coat material containing at least seven major antigens. Infection with the virus induces both antibody and T cell responses, and life-long immunity. On entry into the cell, the viral coat is digested and early and late mRNA are transcribed within 7 hours. Production of host proteins in the cell is stopped during synthesis of the virus and transcription ceases by approximately 7 hours. The host cells usually undergo lysis with release of viral particles, but some viral

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particles can leave intact infected cells [21]. Viral proteins are expressed on the cell surface by 1 to 2 hours after infection and may induce killing of the target cell by cytotoxic T cells [22,23]. The presence of viral antigens in the host cell membranes and organelles is believed responsible for induction of strong helper activity for induction of immune responses to weak tumor antigens [24]. Studies in melanoma patients by J. C. Belisario and G. W. Milton [25] showed that injection of vaccinia virus into cutaneous metastases in seven patients resulted in regression of the metastases. Systemic responses against noninjected nodules were also seen in five of the patients. K. H. Burdick and W. A. Hawk [26] reported that intralesional injection of vaccinia virus was associated with regression of both cutaneous and regional LN metastases. Another three patients showed temporary improvement and five showed no response. Similar studies were reported by H. H. Roenijk et al [27]. J. D. Everall et al [28] injected vaccinia virus into primary melanoma 14 days prior to surgical excision and reported that 23 patients so treated had improved RFS compared with 25 patients treated by surgical excision alone. M. K. Wallack et al [29] used vaccinia viral lysates of cancer cells to immunize patients. Studies in 29 patients with various cancers showed the procedure to be safe and to be associated with lack of disease progression in nine patients. Antibodies against melanoma lines were induced in melanoma patients undergoing this treatment [30]. Phase I and II studies by the Southeastern Oncology Group were conducted in 48 patients with resected high-risk primary and lymph node metastases using a vaccine prepared from vaccinia virus-induced lysates of four melanoma cells [31]. These studies led to a randomized controlled trial on 217 patients that had its final report in 1998 [5]. There was no significant increase in overall (p ⳱ 0.79) or disease-free survival (p⳱0 .61) in the patients treated with the vaccine. In view of the promising experimental and clinical results from earlier studies on vaccinia virus, we initiated in 1984 a series of Phase II studies in patients with AJCC Stage IIB and III melanoma to determine whether immunization with vaccinia melanoma cell lysates (VMCL) over a 2-year period may have therapeutic efficacy. The first of these trials indicated a highly


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significant difference in survival for 80 patients treated with VMCL compared with the survival of 151 historical and 56 concurrent nonrandomized controls [32]. The second Phase II study examined whether pretreatment of patients with cyclophosphamide improved results any further. This was prompted by previous reports that pretreatment with cyclophosphamide increased cell-mediated immunity to an autologous melanoma vaccine [33]. Again, the survival of 102 patients treated with VMCL plus cyclophosphamide was significantly above that of the historical controls but was no better than the group of patients treated with VMCL alone [34]. The vaccine appeared highly immunogenic in terms of antibody production in the patients [35,36] and electron microscopy confirmed the particulate nature of the vaccine [35] and the presence of viral material in the membrane fragments used. The results from the Phase II studies prompted a randomized, controlled trial, which was initiated in 1988 within Australia to test the efficacy of the vaccine against a control group treated only by surgery. An interim analysis of this trial [37] after accrual of 569 patients in 1996 indicated a difference in favor of the VMCL-treated group that was not significant. RESULTS FROM THE RANDOMIZED TRIAL ON VACCINIA MELANOMA CELL LYSATES VACCINE IN TREATMENT OF STAGE IIB AND III MELANOMA Preparation of VMCL for vaccine production was carried out by methods similar to those described by M. K. Wallack et al [31] except that one melanoma line was used instead of four melanoma lines as used by Wallack. The vaccine contained the centrifuged material from the vaccinia viral lysate of MM200 melanoma cells. The particulate nature of the vaccine is shown in Figure 1. The line chosen contained the main melanoma differentiation antigens known to induce responses against melanoma. Prior studies on antibody responses to melanoma had shown that sera from melanoma patients frequently reacted to this particular melanoma line [15,38]. Further details of vaccine production, patient selection, study design, and statistical analysis of the trial are described elsewhere [39].

Figure 1 Electron micrograph of ultracentrigued deposit from vaccinia melanoma cell lysates. A. Vaccinia virus ⳯ 5000. B. Membranous structures ⳯ 20,000. C. Membranous structures ⳯ 30,000.

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Seven hundred patients were accrued into the study from four main centers in Australia. Median follow-up at the time of analysis was 8 years. Accrual into the different prognostic strata is shown in Figure 2 and patient characteristics are summarized in Table 1. Twenty-five patients were considered ineligible for various reasons. These were evenly distributed between the groups. Relapse-free survival and OS were as shown in Table 2. Overall survival by Kaplan-Meier estimates is shown for treated and control groups in Figure 3. Median OS for the control group was 88 months (Figure 3A) and approximately 151 months for the treated group. The univariate stratified analysis of OS after exclusion of the 25 ineligible and two untreated patients showed a P value of 0.068. No multivariate analysis model indicated statistical significance for treatment allocation. The point estimate of the hazard ratio (HR) (0.81) indicated approximately a 20% reduction in risk of dying from

Figure 2 The number and percentage of patients accrued into each stratum. Sixty percent of the patients (stratum 4 and 5) had detection of nodal metastases 8 weeks or more after removal of the primary.

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Table 1 Patient Characteristics

n All patients 700 (48%) VMCL 353 (48%) Control 347 (48%)

Median age (years)

Gender M

F

Median tumor thickness (mm) Ulceration*

51

471 (67%) 217 (33%)

2.7

335/70

51

222 (63%) 125 (37%)

2.7

168/35

50

249 (71%)

2.7

167/34

92 (29%)

* Ulceration was not recorded in 78 and 83 of the patients in vaccinia melanoma cell lysate (VMCL) and Control Group, respectively. These were recorded as not ulcerated in the table.

Table 2 Relapse-Free and Overall Survival Median Median Total Eligible Patients All Patients 673 48.4 VMCL 338 53.4 Control 335

5 Years

10 Years

RFS* OS** RFS Alive Dead (years) (years) %

OS %

RFS %

OS %

379

294

4.4

9.3

49.1

57.7

43.9

201

137

6.9

12.6

50.9

60.6

45.4

178

157

3.6

7.3

46.8

54.8

42.5 41

Stratified Cox regression univariate analysis of treatment. Eligible Patients * P ⫽ 0.17; HR ⫽ 0.86; CI ⫽ 0.70–1.07. ** P ⫽ 0.068; HR ⫽ 0.81; CI ⫽ 0.64–1.02. VMCL ⫽ vaccinia melanoma cell lysate; RFS and OS ⫽ relapse-free and overall survival; HR ⫽ hazard ratio; CI ⫽ 95% confidence intervals.


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Figure 3 Kaplan Meier estimates of overall survival of eligible patients. The numbers at risk are indicated for control (top line) and vaccinia melanoma cell lysate-treated patients.

melanoma in the treated group. The 95% confidence limits, however, included 1.0 (Table 2). At 5 years and 10 years, there were 5.8% and 12.4% survival difference respectively in favor of the treated group. The median RFS were 43 and 83 months in the control and treated groups respectively (p ⳱ 0. 1 7). The treatment was not associated with significant toxicity. DISCUSSION OF THE RESULTS The results indicate that immunotherapy with VMCL was associated with a nonsignificant trend to improvement in OS that amounted to a 20% reduction in the risk of dying when assessed by hazard ratios. The confidence limits, however, in-

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cluded 1.0, indicating this may have been a chance finding. The lack of any significant effect on RFS makes this a possible explanation of the results. Nevertheless, the size of the estimated effects on survival (as illustrated by an increase in estimated median survival from 88 months to 151 months or a 10% increase in absolute survival at 5 years) would, if true, be important. Similarly, the treated group had a 14% reduction in the HR for development of recurrences that, if carried through to a similar reduction in the risk of death, would represent worthwhile clinical benefit. When viewed in these terms and given the negligible toxicity of the vaccine, a useful clinical benefit from the vaccine remains a possibility. Even though the trial included approximately 700 patients and had a median follow-up of 8 years, the number of deaths (n ⳱ 294) was relatively low and the results need to be reviewed after a longer follow-up. Subset analysis did not reveal benefit from treatment in any particular group of patients. The best interpretation of the results is that immunization with the vaccine produced a true increase in survival of approximately 20%. The relatively low statistical significance of the difference (p ⳱ .068) could be because of the wide variation in survival of individual patients and the resulting wide confidence limits. Nevertheless, the therapeutic results were much less than expected based on the Phase II studies, in which the median survival of the historical and nonrandomized control group was 32 months and the median survival of the treated group had not been reached with a minimum follow-up period of 5 years [32]. The main reason for this may be the improved survival of all patients in the study compared with the historical controls. This improvement in survival of patients occurred throughout the duration of the trial and Cox regression analysis showed that this was a more powerful factor than the effect of treatment. It is not uncommon for the control group in Phase III studies to have much better survivals than the control groups in Phase II studies. Nevertheless, the improved survival of the control patients on this study appears remarkable, given that at the commencement of this study, the published 5-year survival rates for patients with AJCC Stage IIB and Ill disease ranged from 23 to 42 months and median survivals

80

151

217

700

427

280

642

IIB,III

IIB,III

III

IIB,III

III

IIB,III

IIB,III

n

72

34

31

88

41

32

Controls

6**

46**

36**

151**

50**

10

⬎60

26

11

0

23

0

2

(%)

T4 N0

Treated

Median tumor

—

2.7

—

1.98

2.0

thickness (mm)

38

16.8

48

37

31

26

(%)

Ulceration

33

89

45

58

38

45

(%)

1LN

41 (0.8)

32 (1.4)

44 (1.3)

60 (.63)

45 (1.0)*

%

ⱖ2LNs

* Figures in brackets indicate proportion of patients with l involved LN. ** P values for OS were 0.79, 0.068, 0.50, 0.024, and 0.74 for studies by Wallack et al, vaccinia melanoma cell lysates (VMCL) Phase III. Eastern Cooperative Oncology Group (ECOG) 1684 and ECOG 1690, respectively. ??? WHO ⫽ World Health Organization.

VMCL Phase II (1987) Historical Controls (SMU) (1980–84) Wallack et al (1995) VMCL Phase III (2000) WHO No 16 (1996) ECOG 1684 (1996) ECOG 1690 (2000)

Stage

Median survivals (months)

Table 3 Median Overall Survival of Patients in Control and Treated Groups and Comparison of Key Prognostic Factors in Recent Melanoma Vaccine and Interferon Adjuvant Trials

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ranged from 32 to 36 months (7,40–42). In more recent studies, listed in Table 3, the median survivals of patients in control groups in the ECOG 1684 [4] and World Health Organization 16 [8] IFN␣-2a trials were 34 and 31 months, respectively, and 41 months in the immunotherapy trial of M. K. Wallack et al [5]. The most recent ECOG 1690 IFNcx-2a trial, however, reported a median survival of 72 months, which was closer to the 88 months recorded in the present study [6]. One of the practical consequences of the improved survival of the patients in the study was the impact it had on the trial design, in that many more patients were needed to detect a difference in survival. The study was therefore underpowered to detect small differences in survival. Despite the relatively small benefits from the treatment with VMCL, it is worth noting that the results (if not attributable to chance) are the best yet reported from randomized trials of melanoma vaccines in the adjuvant setting. In the H. K. Wallack study, the differences in median survivals of treated (50.2 months) and control (41 .3 months) groups were quite small and not significant [5]. The vaccine and the protocol used by Wallack et al were different from those used in our studies and the control group was given vaccinations against vaccinia alone. Whether the latter may have had some beneficial effects is unknown but cannot be discounted. The GM2/ KLH vaccine developed by Livingston et al was found to be less effective than high-dose IFN [10]. An allogeneic vaccine, ‘‘Melacine,’’ given with an adjuvant ‘‘Detox’’ to patients with AJCC Stage IIA melanoma also failed to have any effect on disease-free survival [43]. Subgroups of patients in the latter study who were human leukocyte antigen-A2 or -C3 had highly significant prolongation of disease-free survival [44]. WHY WERE THE VACCINIA VIRAL LYSATE VACCINES NOT MORE EFFECTIVE? Much more is now known about melanoma antigens and design of vaccines than when these studies were started in 1984. Viral lysates, however, continue to have many properties that make them attractive as vaccines; e.g., the antigens are particulate rather than soluble so they are more likely to be taken


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up by antigen-presenting cells, such as dendritic cells (DCs). The vaccines were given intradermally, so it is likely that DCs took up the lysates and transported them to the regional LNs. Increased size and tenderness of regional LNs draining the vaccination site were common in the patients, especially in the first 6 to 8 weeks, suggesting that stimulation of regional LNs occurred. Studies since 1984 have also shown that T cell responses may be directed to antibody (Th2) rather than representing cell-mediated (Th1) responses. Antibody-related responses may be more frequent following repeated antigenic stimulation, as may occur in tumor-bearing patients. Cell-mediated responses are more likely in response to viruses such as vaccinia, which could be expected to preferentially favor TH1 IC responses to the vaccine. Unfortunately, these studies were initiated before assays to measure Th1 and Th2 responses were available, so whether TH1 responses were initiated by VMCL injections is not known. It is clear, however, that the vaccine induced immunoglobulin-G lymphocyte-dependent antibody responses against melanoma in the patients [24]. Studies on antibody responses showed that induction of the response was rapid, with peak titers at approximately 4 weeks, but following this, antibody titers declined (Figure 3). The reason for this is not clear but raises the possibility that vaccine administration induced regulatory T cells, as reported by others [45]. Induction of the latter is poorly understood but we have shown that heavy-chain ferritin from melanoma cells may induce regulatory T cells [46,47]. They may also be induced during immunization with self-antigens and during frequent vaccine administration, as would have occurred in this study. Future studies may need to pay more attention to the activity of these cells and methods to inhibit their activity, particularly their production of interleukin-10. Another question is whether the vaccinia MM200 lysate contained melanoma antigens known to be associated with cytotoxic T lymphocytes (CTL) cell responses against melanoma. Studies in animal models suggest that antigens specific to individual tumors may be the most effective for rejection of tumors and some recent vaccine trials have used autologous vaccines in the hope of generating such responses. These anti-

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gens would not have been present in the VMCL vaccine or in other allogeneic melanoma cell vaccines. Nevertheless, the vaccine did contain the common melanoma antigens known to be frequently recognized by T cells. These included the differentiation antigens tyrosinase, gpl00, and MART-I, and the tumor-specific antigens MAGE-A3, MAGE-Al0, BAGE, GAGE, and XAGE. It did not contain MAGE-l, CT7, NA17-l, or NYESO-l (unpublished data). Studies on a limited number of patients treated with VMCL off study have shown induction of

Figure 4 LDA activity of sera taken from patient J.Bl, before, and at 4 and 12 weeks during immunizations with vaccinia melanoma cell lysate. FH-Mel and P(MP)-Mel are two allogeneic melanoma cells and FH-EBV and P-EBV are Epstein-Barr virus (EBV)-transformed B cells from these patients. Baseline release from the target cells alone are shown by the target cell designations and the 51Cr release in the presence of the effector cells caused by their natural killer activity is shown by the dashed lines. 51Cr release above these lines in the presence of (heat-activated) sera is attibutable to LDA activity. Human leukocyte antigen phenotype of Mel-MP was A.24.ⳮ: B 7.60: DR 2.4 and EBV-FHA 2.24: B 35.60: Dr 4.ⳮ.


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CTL activity against gpl00 280, MART-l, tyrosinase, and MAGE-3A2 (as shown in Figure 5). Vaccinia melanoma cell lysates were at least as effective as the human leukocyte antigen-A2 epitope peptides from these antigens in inducing responses against these melanoma epitopes. The figure shows, however, that IFN-␥ production was not induced in all patients. Unfortunately, measurement of T cell responses against these antigens was not possible during the course of the VMCL trial, so we were unable to correlate CTL responses or lack of them with the clinical course of individual patients. MORE GENERAL ISSUES IN USE OF MELANOMA VACCINES Recent studies suggest that the number of T cells against melanoma may be increased by immunizing patients after lymphocyte depletion [48,49]. Our phase II study after relatively low doses of oral cyclophosphamide did not show any benefit in patient survival, but this issue needs to be studied more carefully. Adoptive transfer studies with cloned T cells or tumor-infiltrating lymphocytes have shown that migration of T cells into the tumor is limited and fewer than 0.005% of transferred lymphocytes actually reached the tumor. Methods to increase T cell infiltration are being explored. Lymphocyte migration is a two-step process, with the first step being adhesion of lymphocytes to ligands on endothelial cells induced by inflammation, such as intercellula adhesion molecule (ICAM1) binding to selectins [50]. The second step is migration in response to chemokines. W. H. Kershaw et al [51] suggested that growth-regulated oncogene alpha [52] is produced selectively by melanoma and that transfection of its chemokine receptor CXCR2 into T cells may aid localization in melanoma. Apart from issues related to vaccine design and administration, we have been increasingly interested in the hypothesis that melanoma in patients has been selected by the immune system to be resistant to host defenses. The escape mechanisms may be multiple and vary among patients and different tumors in patients [53,54]. The immune system appears to kill tumor cells by induction of apoptosis and induction of resistance to apoptosis in melanoma cells may be a fundamental

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Figure 5 Interferon (IFN)-␥ production from blood lymphocytes of two patients during immunotherapy with vaccinia melanoma cell lysates vaccine. PBL from BT but not SM showed good responses to peptide epitopes from MAGE3-A2, gp100 280-9V and MART-1. PBL (5 ⳯ 105) were incubated for 20 hours with 5 ⳯ 105 T2 target cells that had been pretreated with the peptides at 10 ␮g/mL for 2 hours then washed two times. Supernatants were assayed for IFN-␥ using the IFN-␥ Eliza kit from Pharmingen (Catalog No. 554548). Peptides used were MAGE3-A2 FLWGPRALV, gp100 280-9V YLEPGPVTV, MART-1 ELAGIGILTV, and Tyrosinase YMDGTMSQV (unpublished data).

escape mechanism [55]. Our studies on the mechanism of resistance of melanoma cells to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand have revealed several different mechanisms, such as loss of death receptors or inhibition by intracellular Bcl-2 family proteins and inhibitor-of-apoptosis family proteins [54–56]. Therapeutic approaches to overcome these apoptosis-resistance mechanisms


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are becoming available and may be valuable adjuncts to treatment with melanoma vaccines. In conclusion, the use of viral lysates to treat patients with melanoma may be as effective as more recent vaccine approaches to induce immune responses against melanoma. Limitations of the vaccines may be those that apply to the efficacy of tumor vaccines in general. New approaches might include lymphocyte depletion to increase the number of specific memory T cells and reduce or control regulatory T cells. In addition, imaginative approaches may be needed to facilitate homing of T cells to the site of small, extravascular, ‘‘immunologically silent’’ foci of melanoma cells. Combination of these approaches with methods to sensitize melanoma cells to apoptosis may result in much-needed improvement in treatment of the disease. REFERENCES 1. Balch CM, Buzaid AC, Soong SJ, Atkins MB, Cascinelli N, Coit DG, Fleming ID, Gershenwald JR, Houghton A, Kirkwood JM, McMasters KM, Mihm MF, Morton DL, Reintgen DS, Ross MI, Sober A, Thompson JA, Thompson JF. Final version of the American Joint Committee on Cancer staging system for cutaneous melanoma J Clin Oncol 2001; 19:3635–3648. 2. Balch CM, Soong S-J, Gershenwald JE, Thompson JF, Reintgen DS, Cascinelli N, Urist M, McMasters KM, Ross ML, Kirkwood JM, Atkins MB, Thompson JA, Coit DG, Byrd D, Desmond R, Zhang Y, Liu P-Y, Lyman GH, Morabito A. Prognostic factors analysis of 17,600 melanoma patients: validation of the American Joint Committee on Cancer Melanoma Staging System J Clin Oncol 2001; 19:3622–3634. 3. Dickler MN, Coit DG, Meyers ML. Adjuvant therapy of malignant melanoma Surg Oncol Clin N Am 1997; 6:793–812. 4. Kirkwood JM, Strawderman MH, Ernstoff MS. lnterferonalpha-2b adjuvant therapy of high-risk resected cutaneous melanoma: the Eastern Cooperative Oncology Group Trial EST 168 J Clin Oncol 1996; 14:7–17. 5. Wallack MK, Sivanandham M, Balch CM, Urist MM, Bland KI, Murray D, Robinson WA, Flaherty L, Richards JM, Bartolucci

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AA, Rosen L. Surgical adjuvant active specific immunotherapy for patients with stage III melanoma: the final analysis of data from a phase III. randomized, double-blind, multicenter vaccinia melanoma oncolysate trial J Am Coll Surg 1998; 187: 69–77. 6. Kirkwood JM, Ibrahim JG, Sondak VK, Richards J, Flaherty LE, Ernstoff MS, Smith TJ, Rao U, Steele M, Blum RH. Highand low-dose Interferon alpha-2b in high-risk melanoma: first analysis of intergroup trial E1690/S91 I 1/C9190 J Clin Oncol 2000; 18:2444–2458. 7. Veronesi U, Adamus J, Aubert C, Bajetta E, Beretta G, Bonadonna G, Bufalino R, Cascinelli N, Cocconi G, Durand J, De Marsillac J, Ikonopisov RL, Kiss B, Lejeune F, MacKie R, Madej G, Mulder H, Mechl Z, Milton GW, Morabito A, Peter H, Priario J, Paul E, Rumke P, Sertoli R, Tomin R. A randomized trial of adjuvant chemotherapy and immunotherapy in cutaneous melanoma N Engl J Med 1982; 307:913–916. 8. Cascinelli N. Evaluation of efficacy of adjuvant rIFN 2A in melanoma patients with regional node metastases Proc American Society for Clinical Oncology (ASCO) 1995; 14:A129. 9. Cascinelli N, Bufalino R, Morabito A, MacKie R. Results of adjuvant interferon study in WHO melanoma programme Lancet 1994; 343:913–914. 10. Kirkwood JM, Ibrahim JG, Sosman JA, Sondak VK, Agarwala SS, Ernstoff MS, Rao U. High-dose interferon alfa-2b significantly prolongs relapse-free and overall survival compared with the GM2-KLH/QS-21 vaccine in patients with resected stage jib-iii melanoma: results of intergroup trial e1694/s9512/ c509801 J Clin Oncol 2001; 19:2370–2380. 11. Hersey P, Balch CM. Current status and future prospects for adjuvant therapy of melanoma Aust N Z J Surg 1984; 54: 303–315. 12. McGovern VJ. Spontaneous regression of melanoma. Pathology 1975; 7:91–9. 13. Hersey P, Murray E, Grace J, McCarthy WH. Current research on immunopathology of melanoma: analysis of lymphocyte populations in relation to antigen expression and histological features of melanoma Pathology 1985; 17:385–391.


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25. Belisario JC, Milton GW. The experimental local therapy of cutaneous metastases of malignant melanoblastomas with cow pox vaccine or colcemid (demecolcine or omaine) Aust J Dermatol 1961; 6:113–118. 26. Burdick KH, Hawk WA. Vitiligo in a case of vaccinia virustreated melanoma Cancer 1964; 17:708–712. 27. Roenigk HH, Deodhar S, St. Jacques R, Burdick K. Immunotherapy of malignant melanoma with vaccinia virus Arch Dermatol 1974; 109:668–673. 28. Everall JD, O’Doherty CJ, Wand J, Dowd PM. Treatment of primary melanoma by intralesional vaccinia before excision Lancet 1975; 27:583–587. 29. Wallack MK, Steplewski Z, Koprowski H, Rosato E, George J, Hulihan B, Johnson J. A new approach in specific, active immunotherapy Cancer 1977; 39:560–564. 30. Wallack MK, Michaelides M. Serologic response to human melanoma lines from patients with melanoma undergoing treatment with vaccinia melanoma oncolysates Surgery 1984; 96: 791–800. 31. Wallack MK, McNally KR, Leftheriotis E, Seigler H, Balch C, Wanebo H, Bartolucci AA, Bash JA. A southeastern cancer study group phase I/II trial with vaccinia melanoma oncolysates Cancer 1986; 57:649–655. 32. Hersey P, Edwards A, Coates A, Shaw H, McCarthy W, Milton G. Evidence that treatment with vaccinia melanoma cell lysates (VMCL) may improve survival of patients with stage II melanomia Cancer Immunol Immunother l987[??]; 25:257–265. 33. Berd D, Maquire HC, Mastrangelo MJ. Induction of cellmediated immunity to autologous melanoma cells and regression of metastases after treatment with a melanoma cell vaccine preceded by cyclophosphamide Cancer Res 1986; 46: 2572–2577. 34. Hersey P. Active immunotherapy with viral lysates of micrometastases following surgical removal of high risk melanoma World J Surg 1992; 16:251–260. 35. Hersey P, Edwards A, D’Alessandro G, MacDonald M. Phase II study of vaccinia melanoma cell lysates (VMCL) as adjuvant


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46. Gray CP, Franco AV, Arosio P, Hersey P. Immunosuppressive effects of melanoma-derived heavy-chain ferritin are dependent on stimulation of IL-10 production Int J Cancer 2001; 92: 843–850. 47. Gray CP, Arosio P, Hersey P. Heavy chain ferritin activates regulatory T cells by induction of changes in dendritic cells Blood 2002; 99:3326–3334. 48. Dudley ME, Wunderlich JR, Robbins PF, Yang JC, Hwu P, Schwartzentruber D, Topalian SL, Sherry R, Restifo NP, Hubicki AM, Robinson MR, Raffeld M, Duray P, Seipp CA, RogersFreezer L, Morton KE, Mavroukakis SA, White DE, Rosenberg SA. Cancer regression and autoimmunity in patients after clonal repopulation with antitumor lymphocytes Science 2002; 298:850–854. 49. Asavaroengchai W, Kotera Y, Mule JJ. Tumor lysate-pulsed dendritic cells can elicit an effective antitumor immune response during early lymphoid recovery Proc Natl Acad Sci U S A 2002; 99:931–936. 50. Schadendorf D, Heidel J, Gawlik C, Suter L, Czarnetzki BM. Association with clinical outcome of expression of VLA-4 in primary cutaneous malignant melanoma as well as P-selectin and Eselectin on intratumoral vessels J Natl Cancer Inst 1995; 87: 366–371. 51. Kershaw MH, Wang G, Westwood JA, Pachynski RK, Tiffany HL, Marincola FM, Wang E, Young H, Murphy PM, Hwu P. Redirecting migration of T cells to chemokine secreted from tumors by genetic modification with CXCR2 Hum Gene Ther 2002; 13:1971–1980. 52. Haghnegahdar H, Du J, Wang D, Strieter RM, Burdick MD, Nanney LB, Cardwell N, Luan J, Shattuck-Brandt R, Richmond A. The tumorigenic and angiogenic effects of MGSA/GRO proteins in melanoma J Leukoc Biol 2000; 67:53–62. 53. Hersey P. Impediments to successful immunotherapy Pharmacol Ther 1999; 81:111–119. 54. Hersey P. Advances in the non-surgical treatment of melanoma Expert Opin Investig Drugs 2002; 1l:75–85. 55. Hersey P, Zhang XD. How melanoma cells evade TRAIL-induced apoptosis Nature Rev 2001; l:142–150. 56. Hersey P, Zhang XD. Overcoming resistance of cancer cells to apoptosis J Cell Physiol 2003; 196:9–18.

11 Fusogenic Oncolytic Herpes Simplex Viruses for Therapy of Solid Tumors XINPING FU, MIKIHITO NAKAMORI, and XIAOLIU ZHANG Center for Cell and Gene Therapy, Departments of Pediatrics, Molecular Virology and Microbiology, Baylor College of Medicine Houston, Texas

HERPES SIMPLEX VIRUS INFECTION AND REPLICATION: AN OVERVIEW Herpes simplex virus type 1 (HSV-1) is a member of the family Herpesviridae, which includes other well-known human herpesviruses, such as HSV type 2, cytomegalovirus, varicella zos713

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ter virus, and Epstein-Barr virus. Among them, HSV-1 is the most extensively studied and therefore the more thoroughly understood human herpesvirus [1]. During natural infection, HSV-1 usually enters its host through skin or mucosal surfaces. The HSV envelope, a lipid bilayer derived from host cell membrane, contains at least 11 viral glycoproteins [2]. For most herpesviruses, less than half of the viral glycoproteins are thought to participate in viral entry. The initial attachment of HSV to cells is mediated by interaction of glycoprotein C (gC) and/or glycoprotein B (gB) with cell-surface glycosaminoglycans, primarily heparan sulfate [3]. This initial virus-cell contact is not sufficient to trigger virus entry, but apparently is required to position the virus for interaction with receptors recognized by glycoprotein D (gD), including HVEM (a member of the tumor necrosis factor-receptor family) and nectin-1 or nectin-2 (two related members of the immunoglobulin superfamily). The binding of gD to one of its receptors, with the participation of gB and gH-gL heterodimers, activates pH-independent viral membrane fusion, leading directly to internalization of the viral nucleocapsid and tegument into the cell cytoplasm. After productive infection and local replication at the mucosal surfaces, the virus enters sensory nerve endings and then migrates by retrograde axonal transportation to the neuronal cell bodies [4–6]. Here, a more restricted replication cycle occurs, most often culminating in latent infection of these neurons [7,8]. Once latency is established, viral gene expression becomes severely restricted and viral replication ceases, with only the latency-associated transcripts being abundantly transcribed [9]. During latency, the viral genome exists predominantly in an episomal form within the nuclei of neurons [10], and the ends of the virion genomic DNA are covalently joined [11–13]. A variety of stimuli can reactivate the latent virus, which then travels via the axons to the mucosal surfaces, where it produces a new round of infection. Like that of many DNA viruses, the transcriptional program of HSV-1 is a regulated cascade in which early and late phases of gene expression are separated by viral DNA synthesis [14]. The immediate early genes are mainly involved in

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gene regulation, whereas the products of early genes are essentially required for HSV DNA replication. Both immediate and early genes are transcribed before the initiation of viral DNA replication. Late genes, which largely function as structural proteins, are expressed at high levels only after viral DNA replication has taken place. Late transcripts can be further categorized as leaky-late, which are readily detectable before the onset of viral genome replication, or strict late, which are reliably detectable only after the onset of viral DNA replication [15–17]. The HSV genome is a 152-kilobase (kb) double-stranded DNA molecule with approximately 80 open reading frames [18]. It comprises two covalently linked segments, designated as long (L) and short (S). Each segment consists of unique sequences (UL and US ), each bracketed by inverted repeats [19]. There are three internal origins of replication along the viral genome, one located in the long segment (OriL) and a diploid origin (OriS) in the repeated region bracketing the short segment [1]. Seven of the gene products encoded by the virus are necessary and sufficient for origin-dependent viral DNA replication [20–23]. They include a DNA polymerase (UL30), a protein designated ICP8 (UL29) that binds to singlestranded DNA, an origin-binding protein (UL9) that binds specifically to multiple sites at or near the replication origins of the viral genome, a double-strand DNA-binding protein (UL42) that also forms complexes with the DNA polymerase, and three additional proteins (UL5, UL9, and UL52) that form a complex in equimolar ratios and function as a primase or helicase in the presence of UL29. During HSV replication, the termini of the input liner viral genome fuse soon after infection. The circularized DNA molecules then serve as templates for the synthesis of concatemeric DNA, by a rolling-circle mechanism. Viral assembly begins in the nuclei of infected cells, where unit-length progeny genomes are thought to be cleaved from the concatemeric intermediates and packaged into viral capsids. Mature viruses are formed when these capsids traffic through the cytoplasm and bud into an organelle, such as the Golgi network, and acquire their final envelope [24].

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DEVELOPMENT OF ONCOLYTIC HERPES SIMPLEX VIRUS FOR TUMOR THERAPY Human viruses, including HSV, have the natural ability to efficiently infect and kill target cells. Because viruses can be genetically engineered to kill tumor cells while sparing normal cells, they afford an attractive approach to antitumor therapy. Oncolytic viruses have two principal advantages. First, unlike conventional chemotherapy and radiotherapy, they specifically target cancer cells because of their restricted ability to replicate in normal cells [25–27]. Second, compared with replication-incompetent vectors, oncolytic viruses can propagate from initially infected tumor cells to surrounding tumor cells, thereby achieving a large volume of distribution and enhanced antitumor effects. HSV has been modified for oncolytic purposes, most commonly by deleting viral genes necessary for efficient replication in normal (nondividing) cells but not tumor cells. Deletion of the viral r34.5 gene, which functions as a neurovirulence factor during HSV infection [28], blocks viral replication in nondividing cells [29–31]. The viral ICP6 gene encodes the large subunit of ribonucleotide reductase, which generates sufficient deoxynucleoside 5’-triphosphate (dNTP) pools for efficient viral DNA replication [32–34], and is abundantly expressed in tumor cells but not in nondividing cells. Consequently, viruses with a mutation in this gene can preferentially replicate in and kill tumor cells. The oncolytic HSV G207, which has been extensively tested in animal studies and is currently in clinical trials, harbors deletions in both copies of the r34.5 locus and an insertional mutation in the ICP6 gene by the Escherichia coli lacZ gene [35–37]. Alternatively, an oncolytic HSV can be constructed by using a tumor-specific promoter to drive r34.5 or other genes essential for HSV replication [38]. Compared with other viruses that have been investigated for oncolytic purposes, HSVs possess several unique features that enhance their potential as antitumor agents. First, antiherpetic medications such as acyclovir and gancyclovir are available as safety measures in the event of undesired infection or toxicity from the HSV. Second, productive infection by


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HSV usually kills target cells much more rapidly than infection by other viruses. For example, a HSV can form visible plaques in cultured cells in only 2 days, in contrast to 7 to 9 days for an adenovirus. In vitro studies have also shown that, at a multiplicity of infection of 0.01, a HSV can kill almost 100% of cultured cancer cells in 2 days [39], whereas a much higher dose or a longer infection time is required to achieve equivalent cell killing with an adenovirus [40]. Rapid replication and spreading among target cells may be vital properties allowing a virus to execute its full oncolytic potential in vivo because the body’s immune mechanism may be more likely to restrict the spread of slower-growing viruses. Third, HSV seems to be able to replicate and spread even in the presence of anti-HSV immunity. This feature has been most clearly demonstrated during recurrent HSV infection, in which the anterogradely transported virus can still grow and spread extensively in the local skin area of infection, despite obvious antiviral immunity. Moreover, pre-existence of anti-HSV immunity in experimental animals has no significant effect on the therapeutic potency of oncolytic HSVs administered either intratumorally or systemically [41–43]. Fourth, HSVs have very wide cell tropism, infecting almost every type of human cell tested so far. Thus, oncolytic viruses derived from HSV would likely have wide applicability among cancer patients. Finally, the risk of introducing an insertional mutation during HSV oncolytic therapy appears minimal because HSVs generally do not integrate into cellular DNA. Oncolytic HSVs were initially designed and constructed for the treatment of brain tumors—glioblastomas in particular [37,44]. Subsequently, they have proved to be effective in treating a variety of other human solid tumors, including breast cancer [39,45]. The safety of the oncolytic virus G207 has been extensively tested in mice [46] and a primate species (Aotus) that is extremely sensitive to HSV infection [47,48]. These studies have confirmed that oncolytic HSVs are safe for in vivo administration. These encouraging results in animals have prompted clinical trials of these viruses in patients with malignant gliomas [49,50].

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STRATEGIES TO ENHANCE THE POTENCY OF ONCOLYTIC HERPES SIMPLEX VIRUSES Despite encouraging preclinical results, the available evidence indicates that current oncolytic viruses, although safe, may have only limited antitumor activity on their own. For example, although such viruses inhibited tumor growth and improved the survival of experimental animals bearing human tumor xenografts [35,37,43,45,51], they effected cure in only a fraction of the animals. In ongoing Phase I and II clinical trails, several oncolytic viruses have been well-tolerated and have produced some evidence of antitumor effect. However, it is evident that the therapeutic efficacy of these viruses must be improved before significant changes in the tumor growth curve, and hence prognosis, are seen [49,50,52]. The suboptimal efficacy of oncolytic viruses may be attributable to viral gene deletions, which can reduce the replicative potential of the virus in tumors. Deletion of the ␥34.5 gene, for example, significantly reduces virus replication even in rapidly dividing cells [31,53–55]. Thus, strategies to enhance the potency of current oncolytic viruses appear warranted. Attempts to improve the antitumor activity of oncolytic HSVs have included their combined administration with radiotherapy and chemotherapy [33,56–59] and insertion of immune modulator genes such as IL-4, IL-12, and B7.1 into the viral genome [60–62]. Less successful have been efforts to directly increase oncolytic potency by combining the virus with genes encoding prodrug converting enzymes, such as HSV thymidine kinase (TK) [63,64], most likely because the antitumor effect of prodrug activation is offset by its inhibitory action on viral replication. RATIONALES FOR DEVELOPING FUSOGENIC ONCOLYTIC HERPES SIMPLEX VIRUSES FOR TUMOR THERAPY Several viruses kill their target cells through the formation of multinucleated syncytia, a process that involves membrane fusion between the infected and uninfected cells. The viral


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components contributing to syncytia formation are mainly the fusogenic membrane glycoproteins (FMGs). An attractive antitumor strategy therefore would be to incorporate syncytiaforming capability into an oncolytic HSV, so the virus would kill tumor cells by two efficient and complementary mechanisms: direct cytolysis (through virus replication) and cell membrane fusion. This approach might even yield a synergistic antitumor effect, given that syncytia formation in the tumor tissue can facilitate the spread of virus, leading, in turn, to widespread syncytia formation. Although wild-type HSV isolated from patients does not cause significant cell fusion in vitro, cells infected with certain spontaneously occurring syncytial mutants fuse extensively, either with each other or with uninfected cells [65,66]. Analysis of these syncytial mutants has shown that the syncytia formation results from aberrant expression of several viral glycoproteins, such as gB and gK [66–69]. It is therefore possible that an oncolytic virus capable of conferring a syncytial phenotype could be selected from a well-characterized oncolytic HSV. Furthermore, because certain viral glycoproteins (including gB and gK) are encoded by late genes (␥), the expression of which depends upon viral DNA replication, an oncolytic virus expressing these proteins might retain the safety of the original virus because syncytia formation occurs in tumor cells (where the virus can undergo a full infectious cycle), but not in normal nondividing cells (where viral replication is restricted and little glycoprotein is expressed). Alternatively, a fusogenic oncolytic HSV can be constructed by inserting a fusogenic membrane glycoprotein from another virus into an oncolytic HSV genome, preferably under the control of a tumor-selective promoter. The resultant virus may have advantages over fusogenic viruses directly selected from an HSV. That is, syncytia formation mediated by FMGs relies on the initial binding of these glycoproteins with their specific receptors on target cells, which then induces ordered structural changes of the membrane lipid bilayers, leading to lipid mixing and eventually to membrane fusion either between viral and cellular membranes or among cellular membranes [70]. Because the molecular requirements for viral–cel-

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lular membrane fusion (a prerequisite for virus entry into target cells) and cell–cell membrane fusion (for syncytia formation) are essentially the same, tumor cells that become resistant to virus infection by receptor downregulation or mutation may also be refractory to syncytia formation mediated by the same virus. However, when a FMG from a different virus is incorporated into an oncolytic HSV, it uses a receptor that differs entirely from those normally recognized by HSV glycoproteins. This acquired property should reduce the emergence of therapy-resistant tumor cells because any tumor cells resistant to infection or syncytia formation mediated by HSV would still be destroyed by syncytia formation through the expression of a FMG from a different virus. This is an important consideration because, unlike xenografted tumors established from cultured tumor cells, which are relatively homogenous, the malignant cells in naturally occurring tumors may be heterogeneous in their sensitivity to HSV infection owing to variation among their cell surface receptors. CONSTRUCTION OF FUSOGENIC ONCOLYTIC HERPES SIMPLEX VIRUSES THROUGH RANDOM MUTAGENESIS Previous studies have shown that certain spontaneously occurring HSV syncytial mutants can be isolated in vitro, and are able to fuse extensively either with each other or with uninfected cells [65,66]. To learn whether syncytial mutants can also be selected for oncolytic purpose, X. Fu et al [39] subjected the well-characterized oncolytic HSV G207 to random mutagenesis through incorporation of the thymidine analog bromodeoxyuridine during virus replication in Vero cells. The mutagenized virus stock was then screened for the ability to confer a syncytial phenotype upon infection of Vero cells. Plaques resulting predominantly formed from syncytia formation were collected, and one isolate, designated Fu-10, consistently showed a strong syncytial phenotype after a few consecutive passages. Phenotypic characterization showed that infection with Fu-10 caused widespread syncytia formation in a variety of


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tumor cells of different tissue origins, including A-549 (lung), DU-145 (prostate), HepG2 (liver), MDA-MB-435 (breast), and U-87 MG (glioblastoma). In vitro analysis also showed that Fu-10 had a significantly stronger ability to kill these tumor cells than did G207. Notably, there was a strong correlation between the intensity of syncytia formation and the degree of toxicity toward individual tumor cells during Fu-10 infection. For example, Fu-10 displayed the strongest killing effect in A-549 and HepG2 cells, which also showed the most extensive syncytia formation. In MDA-MB-435 and DU-145 cells, characterized by only modest syncytia formation, twice as many cells were killed by Fu-10 than by G207, when the viruses were used at a dose of 0.1 pfu/cell. Fu-10 showed marginally better killing than G207 in the U-87 MG cell line (28% vs. 44% survival) when the cells were infected at 0.1 pfu/cell, but did not produce any detectable cytotoxicity at a lower dose (0.01 pfu/cell) [39]. In vivo studies showed that Fu-10 is significantly more effective than the nonfusogenic G207 against established metastatic breast cancer in lung. Systemic administration of Fu10 resulted in a significant reduction of lung tumor nodules: The average number of tumor nodules in Fu-10–injected mice was only 2.6 per animal, compared with 22.2 and 69.2 nodules in G207- and PBS- treated groups, respectively. There were no visible tumor nodules in the lungs from two of five mice in the group treated with Fu-10 [39]. These findings demonstrate that Fu-10 has a significantly enhanced oncolytic effect on disseminated metastatic breast cancer after being systemically injected into experimental animals, an outcome predicted by in vitro studies of this fusogenic virus. CONSTRUCTION OF FUSOGENIC ONCOLYTIC HERPES SIMPLEX VIRUS BY INSERTION OF A HYPERFUSOGENIC ENVELOPE PROTEIN OF GIBBON APE LEUKEMIA VIRUS INTO THE VIRAL GENOME Earlier investigations of FMGs for use in cancer treatment relied on viruses whose infections naturally induce syncytia

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formation in target cells. These studies demonstrated that, in principle, administration of these viruses could lead to significant oncolysis; in some cases, tumor destruction by the viruses subsequently elicited potent antitumor immune responses [71]. More recently, A. Bateman et al [72] reported that FMGs delivered either as plasmid DNA or by viral vectors are also extremely cytotoxic to tumor cells. An example is provided by a C-terminal truncated form of the gibbon ape leukemia virus envelope glycoprotein (GALV.fus), which lacks the 16-aminoacid R-peptide of the wild-type protein [72,73], that restricts fusion of the envelope until it is cleaved during viral infection [74]. Hence, truncation of the R-peptide from this glycoprotein leads to a constitutive and hyperfusogenic version of GALV.fus [75]. The cellular receptor for GALV.fus has been identified as Pit-1, a type III sodium-dependent phosphate transporter, and is abundantly distributed on the surface of most mammalian cells [76,77]. Transduction of the GALV.fus gene into a range of human tumor cells efficiently kills the cells through syncytia formation [78], which destroys neighboring cells through a ‘‘bystander’’ effect at least 10-fold greater than that observed with HSV-TK or cytosine deaminase-mediated therapy [78,79]. The full therapeutic potential of GALV.fus will probably not be realized until means are devised for its efficient delivery and specific expression in tumor cells. We hypothesized that this feat might be achieved by inserting the GALV.fus gene into an oncolytic HSV, because oncolytic HSV can specifically replicate and spread in tumor cells. However, because expression of GALV.fus can also cause syncytia formation in normal cells, uncontrolled expression of the gene, even in the context of a tumor-restricted oncolytic virus, still poses a safety concern. This is particularly true when systemic administration is required in cases of metastatic diseases, for example. One way to minimize this risk is to use a tumor- or tissue-specific promoter to control GALV.fus expression. Although many tumor- or tissue-specific promoters have been described, they generally have much lower activity than viral promoters and may lose their tissue specificity once they are cloned into viral vectors [80]. Herpes simplex virus genome transcription is a tightly regulated molecu-


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lar cascade in which early and late phases of gene expression are separated by viral DNA replication [81]. In particular, some of the late transcripts can be characterized as strict-late, the expression of which depends rigorously on the initiation of viral DNA replication. It is therefore possible that directing GALV.fus expression with such a strict-late viral promoter, in the context of an oncolytic HSV, might lead to high-level and selective GALV.fus gene expression in tumor cells. It is expected that such a strict-late viral promoter will be extremely active in tumor tissue, where the oncolytic virus can fully replicate, but silent in normal cells if these are nondividing or postmitotic, because viral replication would be limited [82]. Earlier attempts to clone the GALV.fus gene into an oncolytic adenovirus were not successful [79]. Two reasons may have caused this failure. First, the rapid and widespread formation of syncytia after GALV.fus gene transfection may have interfered with the homologous recombination needed for the genome recombinant of virus. Second, expression of GALV.fus in the context of an adenovirus may have interfered with the infectious process of the virus. Unlike adenoviruses, which are nonenveloped, HSVs are enveloped viruses, infection with which naturally involves membrane fusion. We therefore anticipated that HSVs would be able to withstand the membrane-fusion effect from genes such as GALV.fus and continue to grow. To avoid potential interference from the initial membrane fusion of GALV.fus gene transfection, we used an enforced direct-ligation strategy, which does not require homologous recombination for the cloning of GALV.fus gene into the genome of an oncolytic HSV. As illustrated in Figure 1, fHSVdelta-pac is a bacterial artificial chromosome (BAC)-based construct that contains a mutated HSV genome in which the diploid gene encoding r34.5 was partly deleted, and both copies of HSV packaging signal (pac) were completely deleted [83]. Hence, transfection of this construct into HSV-permissive cells will not form any infectious virus unless an intact HSV pac is provided in cis. Also, any virus generated from this construct will be replication selective because of partial deletion of the r34.5 gene. The gene cassettes were initially linked with a HSV packaging sequence and were then inserted into the

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Figure 1 Schematic illustration of the enforced ligation strategy for insertion of foreign DNA into an oncolytic Herpes simplex virus (HSV). The HSV DNA sequence is represented by hatched areas and the bacterial artificial chromosome (BAC) sequence by black areas (not proportional) in the fHSV-delta-pac. The HSV packaging signal (pac) and the gene cassette (either EGFP or GALV.fus) in a DNA fragment excised from shuttle plasmids are each individually labeled. The gene cassettes together with the pac were ligated onto the BAC–HSV construct in vitro before the ligation mixture was transfected into Vero cells for the generation of infectious viruses.

unique PacI site located in the BAC sequence of fHSV-deltapac. The ligated DNA was directly transfected into Vero cells, to generate Baco-1 (containing EGFP), Synco-1 (containing GALV.fus driven by the IE promoter of CMV), and Synco-2 (containing GALV.fus driven by the UL38 promoter of HSV). Phenotypic characterization of these fusogenic oncolytic HSVs showed clear syncytia formation in all the tumor cells tested, including Hep 3B (liver), DU-145 (prostate), and U87 (breast). The extent of tumor cell fusion did not differ appreciably between Synco-1 and Synco-2. In contrast, the same types of tumor cells infected with Baco-1 lacked this phenotype. In vitro cell killing assay showed that GALV.fus-mediated syncy-


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tia formation in the context of oncolytic HSV replication increased tumor cell killing in these tumor cells [84]. Two experiments were then conducted to determine whether GALV.fus-mediated syncytia formation after Synco-2 infection truly depends on viral DNA replication. First, human tumor cells were infected with either Synco-1 or Synco-2 in the presence or absence of acyclovir, which inhibits HSV DNA replication. Syncytia formation by Synco-1 in Hep 3B cells was largely unaffected by the presence of acyclovir, whereas cell membrane fusion by Synco-2 in the same cells was completely blocked by this drug. Second, to directly test whether Synco-2 loses its ability to cause syncytia formation in normal nondividing human cells, primary human fibroblasts in either a quiescent or cycling state were infected with one of the viruses. The results demonstrated that infection with either Synco-1 or Synco-2 caused syncytia formation in these normal human cells when they were in cycle. Synco-1–mediated cell fusion was only marginally affected in cells whose cycling was slowed by serum starvation or completely arrested by lovastatin. Synco-2–mediated cell fusion, on the other hand, was absent in cells whose cycling was decreased or arrested [84]. These results demonstrate that syncytia formation induced by UL38 promotercontrolled GALV.fus expression in the context of an oncolytic HSV is cell-cycle-dependent. Subsequent animal experiments indicated that the syncytial phenotype and the enhanced ex vivo tumor cell killing shown by Synco-1 and Synco-2 translate into an enhanced antitumor effect in vivo. Both Synco-1 and Synco-2 have significantly better antitumor effects than Baco-1, starting from week 2 after virus administration. However, there was no significant difference in the tumor growth ratio between Synco-1– and Synco-2–treated mice [84]. These results indicate that Synco-2 has equivalent antitumor potency to Synco1, even though its GALV.fus expression is driven by a conditional viral promoter. Histological examination revealed that syncytia comprising a variable number of cell nuclei were frequently encountered across the tissue section of tumors injected with either Synco-1 or Synco-2 virus. Such syncytia

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were not seen in tissue sections of tumors injected with either Baco-1 or PBS. The envelope glycoprotein of human immunodeficiency virus type 1 (HIV-1), which can induce syncytia in the presence of CD4Ⳮ target cells, has recently been cloned into a conditionally replicating adenovirus. In vitro characterization of this virus (Ad5HIVenv) in permissive (CD4-positive) cells showed that syncytium formation induced by this FMG significantly increased the dispersion of viral gene products within the cytoplasm of the syncytial as well as viral particles in the nuclei of the syncytial mass. In addition, progeny virions were released more efficiently from syncytia compared with nonsyncytial cells, facilitating cell–cell spread of the virus particles [85]. These observations are consistent with results obtained from characterization of fusogenic oncolytic HSVs [39], indicating that an oncolytic adenovirus containing a FMG with a wider tropism, if successfully constructed, may also have enhanced antitumor potency in vivo. CONSTRUCTION OF A FUSOGENIC ONCOLYTIC HERPES SIMPLEX VIRUS THAT CONTAINS BOTH FUSION MECHANISMS To further increase the potency of the oncolytic virus, we recently constructed a newer version of fusogenic HSV by incorporating both membrane fusion mechanisms into a single oncolytic HSV, generating Synco-2D. This was achieved through a two-step procedure. Initially, membrane fusion capability was introduced into Baco-1, the nonfusogenic oncolytic HSV, through random mutagenesis [39]. The virus was phenotypically identified and purified to homogeneity. Then the hyperfusogenic GALV.fus gene, driven by the strict-late promoter of the UL38 gene, was cloned into the BAC-based viral genome through an enforced ligation strategy as described earlier, to replace the enhanced green fluorescent protein gene of Baco-1 [86]. The antitumor potency of Synco-2D has been assessed in two tumor models: (1) metastatic ovarian cancer in the abdom-


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inal cavity [86] and (2) prostate cancer in both the orthotopic site and in the lung [89]. Peritoneal invasion of ovarian cancer is a common and serious clinical problem. It has been reported that about 70% of late-stage ovarian cancer patients have metastatic disease in the peritoneal cavity [87]. We therefore chose a peritoneal metastasis model (xenografted Hey-8 cells) as a means to test the efficacy of Synco-2D against human ovarian cancer. Our results demonstrated that intraperitoneal administration of Synco-2D at a moderate dose at a site distant from that of tumor cell implantation has a dramatic therapeutic effect on established ovarian cancer, rendering 75% of animals tumor free. By contrast, none of the animals treated with Baco-1 was tumor-free, and most of the mice in the phosphatebuffered saline (PBS) control group died or became ill and were euthanized during the experiment. The objective of evaluating Synco-2D in a prostate cancer model was twofold. First, we wished to determine whether this doubly fusogenic oncolytic HSV could infect and kill metastatic prostate tumor, which is incurable with conventional therapies. Second, the model afforded the opportunity to compare doubly fusogenic and singly fusogenic HSVs in terms of antitumor efficacy. Both primary and metastatic prostate cancer xenografts were initially established in severe combined immune-deficient mice through orthotopic and systemic injection of PC-3M-Pro4 cells, which were selected from PC-3M cells through repeated cycles of orthotopic inoculation and harvest in athymic mice, and shown to efficiently establish lung metastases after i.v. injection into immune-deficient mice [88]. This tumor xenograft model, representing both primary and metastatic prostate cancer, is more relevant than subcutaneously implanted tumor cells to advanced disease in patients. Our results showed that systemic delivery of Synco-2D had a significantly stronger therapeutic effect than Synco-2 on growth of prostate cancer confined to the primary site. Systemic administration of Synco-2D also produced strikingly better therapeutic effects on lung metastases, indicating that the doubly fusogenic oncolytic HSV is more potent than the singly fusogenic virus, as predicted by its increased activity against cultured tumor cells.

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SAFETY OF FUSOGENIC ONCOLYTIC HERPES SIMPLEX VIRUSES Although oncolytic HSVs replicate only in tumor cells, the syncytia formation by fusogenic oncolytic HSVs is potentially toxic to normal cells and, if uncontrolled, can pose a safety concern, especially the virus is given systemically. During construction of Synco-2 and Synco-2D, several strategies were employed to restrict the syncytia formation to tumor tissues. First, a strictlate viral promoter, UL38p, was used to direct GALV.fus gene expression in both Synco-2 and Synco-2D. The activity of UL38p remains confined to the tumor tissue after systemic administration of an oncolytic HSV [82]. Thus, it is expected that GALV.fus-mediated syncytia formation by these two viruses would be conditionally linked to virus replication in tumor cells. Second, syncytia formation from mutagenized HSV is mainly attributable to aberrant expression of several viral glycoproteins, such as gB and gK [66–69]. Because these glycoproteins are encoded by late genes, the expression of which depends upon viral DNA replication, the cell-membrane fusion mediated by this mechanism would occur in tumor cells (where virus can undergo a full infection cycle) but not in normal nondividing cells (where the virus replication is restricted and very low levels of glycoproteins are expressed). Our findings in previous studies, that blocking viral DNA replication completely abolishes the syncytia-forming ability of Fu-10 (the selected syncytial mutant from G207) [39] and that Synco-2 (containing GALV.fus driven by UL38p) cannot induce syncytia formation in nondividing cells [84], strongly suggest that Synco-2D retains the safety profile of a conventional oncolytic HSV. More comprehensive toxicity studies of these fusogenic oncolytic HSVs in sensitive animals are needed to confirm their safety for clinical use. SUMMARY Oncolytic viruses have shown considerable promise in the treatment of solid tumors, but their potency needs to be im-


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proved if their full clinical potential is to be realized. Recent studies by us and others have shown that the addition of cell membrane fusion activity to an oncolytic virus represents an effective strategy for enhancing the antitumor potency of the virus. In particular, doubly fusogenic oncolytic HSVs have shown increased potency in the treatment of both primary and metastatic tumors after local or systemic administration. Compelling demonstration of the safety of these fusogenic viruses in sensitive animals, including nonhuman primates, is needed to ensure their approval for clinical testing. Most intriguing, perhaps, is the strong likelihood that successful treatment of one type of human solid tumor using fusogenic oncolytic HSVs will translate into successful therapeutic strategies for an array of other human cancers and warrant their future human clinical trails.

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74. Januszeski MM, Cannon PM, Chen D, Rozenberg Y, Anderson WF. Functional analysis of the cytoplasmic tail of Moloney murine leukemia virus envelope protein J Virol 1997; 71: 3613–3619. 75. Forestell SP, Dando JS, Chen J, de Vries P, Bohnlein E, Rigg RJ. Novel retroviral packaging cell lines: complementary tropisms and improved vector production for efficient gene transfer Gene Ther 1997; 4:600–610. 76. Johann SV, van Zeijl M, Cekleniak J, O’Hara B. Definition of a domain of GLVR1 which is necessary for infection by gibbon ape leukemia virus and which is highly polymorphic between species J Virol 1993; 67:6733–6736. 77. Kavanaugh MP, Miller DG, Zhang W, Law W, Kozak SL, Kabat D, Miller AD. Cell-surface receptors for gibbon ape leukemia virus and amphotropic murine retrovirus are inducible sodiumdependent phosphate symporters Proc Natl Acad Sci U S A 1994; 91:7071–7075. 78. Higuchi H, Bronk SF, Bateman A, Harrington K, Vile RG, Gores GJ. Viral fusogenic membrane glycoprotein expression causes syncytia formation with bioenergetic cell death: implications for gene therapy Cancer Res 2000; 60:6396–6402. 79. Diaz RM, Bateman A, Emiliusen L, Fielding A, Trono D, Russell SJ, Vile RG. A lentiviral vector expressing a fusogenic glycoprotein for cancer gene therapy Gene Ther 2000; 7:1656–1663. 80. Babiss LE, Friedman JM, Darnell JE. Cellular promoters incorporated into the adenovirus genome. Effect of viral DNA replication on endogenous and exogenous gene transcription J Mol Biol 1987; 193:643–650. 81. Weir JP. Regulation of herpes simplex virus gene expression Gene 2001; 271:117–130. 82. Fu X, Meng F, Tao L, Jin A, Zhang X. A strict late viral promoter is a strong tumor-specific promoter in the context of an oncolytic herpes simplex virus Gene Ther 2003; 10:1458–1464. 83. Saeki Y, Ichikawa T, Saeki A, Chiocca EA, Tobler K, Ackermann M, Breakefield XO, Fraefel C. Herpes simplex virus type 1 DNA amplified as bacterial artificial chromosome in Escherichia coli: rescue of replication-competent virus progeny and

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packaging of amplicon vectors Hum Gene Ther 1998; 9: 2787–2794. 84. Fu X, Tao L, Jin A, Vile R, Brenner M, Zhang X. Expression of a fusogenic membrane glycoprotein by an oncolytic herpes simplex virus provides potent synergistic anti-tumor effect Mol Ther 2003; 7:748–754. 85. Li H, Haviv YS, Derdeyn CA, Lam J, Coolidge C, Hunter E, Curiel DT, Blackwell JL. Human immunodeficiency virus type 1-mediated syncytium formation is compatible with adenovirus replication and facilitates efficient dispersion of viral gene products and de novo-synthesized virus particles Hum Gene Ther 2001; 12:2155–2165. 86. Nakamori M, Fu X, Meng F, Jin A, Tao L, Bast RCJ, Zhang X. Effective therapy of metastatic ovarian cancer with an oncolytic herpes simplex virus incorporating two membrane-fusion mechanisms Clin Cancer Res 2003; 9:2727–2733. 87. Buy JN, Moss AA, Ghossain MA, Sciot C, Malbec L, Vadrot D, Paniel BJ, Decroix Y. Peritoneal implants from ovarian tumors: CT findings Radiology 1988; 169:691–694. 88. Pettaway CA, Pathak S, Greene G, Ramirez E, Wilson MR, Killion JJ, Fidler IJ. Selection of highly metastatic variants of different human prostatic carcinomas using orthotopic implantation in nude mice Clin Cancer Res 1996; 2:1627–1636. 89. Nakamori M, Fu X, Pettaway CA, Zhang X. Potent antitumor activity after systemic delivery of a doubly fusogenic oncolytic herpes simples virus against metastatic prostate cancer Prostate 2004; 60:53–60.

12 Poliovirus Recombinants Against Malignant Glioma MELINDA MERRILL Department of Molecular Genetics & Microbiology, Duke University Medical Center Durham, NC DAVID SOLECKI Department of Developmental Neurobiology, Rockefeller University New York, NY MATTHIAS GROMEIER Department of Molecular Genetics & Microbiology, Duke University Medical Center Durham, NC

INTRODUCTION Poliovirus has recently been added to the rapidly expanding list of potential viral oncolytic agents. Its inherent tropism for certain malignant cell types, highly lytic growth cycle, and 739

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permissiveness for genetic manipulation qualify poliovirus as a prime target for therapeutic use against cancer. On the other hand, the danger of serious neurological damage following administration of poliovirus-based oncolytic agents restricts its use. We have developed an innovative strategy to harness poliovirus for therapeutic use against central nervous system (CNS) malignancy. Our approach is the result of thorough analyses of the molecular pathogenesis of poliomyelitis and takes advantage of the natural targeting and invasive properties of poliovirus. We have exploited an unconventional mechanism of translation initiation upon which poliovirus relies to achieve a tumor-specific replication phenotype and to exclude viral cytopathogenicity in normal tissues. A prototype oncolytic poliovirus recombinant recently entered production according to ‘‘good manufacturing practice’’ and will undergo toxicology testing in non-human primates. Phase-I clinical trials with our agent against malignant glioma are expected to begin within the near future. POLIOVIRUS MOLECULAR BIOLOGY AND PATHOGENESIS The Poliovirus Life Cycle Poliovirus, a nonenveloped plus-stranded RNA virus, is the prototype member of the Picornaviridae family of viruses. The level of understanding of picornavirus molecular biology is second to none and many aspects of the poliovirus life cycle, schematically represented in Figure 1, have been elucidated. Susceptibility to poliovirus is determined by its sole cellular receptor, the immunoglobulin superfamily (IGSF) molecule CD155 [1]. Binding to CD155 alone is sufficient to induce conformational alteration of the viral particle [2] and results in passage of the virion across the cell membrane and uncoating of the viral RNA genome. Once released from the capsid, the viral RNA serves as a template for viral translation and for negative-strand RNA synthesis (Figure 1). The plus-stranded RNA genome of poliovirus lacks a 5′ cap structure [3] and instead features a 5-terminal covalently linked protein, VPg (4;

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Figure 1 Schematic representation of the life cycle of poliovirus (see text for details).

Figure 1). The viral genome contains an unusually large and highly structured 5′ nontranslated region (NTR) studded with noninitiating AUG codons (Figure 2B). Characterization of the uncommon features of picornaviral 5′ NTRs resulted in the discovery of the internal ribosomal entry site (IRES), that mediates translation initiation in a 5′ end-, cap-independent manner [5,6]. During poliovirus infection, critical determinants of capdependent translation initiation, e.g., the eukaryotic initiation factor 4G (eIF4G) [7] and the poly(A) binding protein (PABP) [8,9] are cleaved by the viral proteinase 2Apro(Figure 2B). Eukaryotic cap-dependent translation relies upon the interaction between PABP and eIF4G (10,11; Figure 2A). The interaction of eIF4G with eIF4E (binding to the cap structure) and PABP results in circularization of mRNAs (12; Figure 2A). Bridging

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Figure 2 A. Proposed model for the circularization of eukaryotic mRNAs. eIF4G, through its affinity for PABP [10,11] and the capbinding factor eIF4E, links the cap-binding complex and the poly(A) tail. B. During poliovirus infection, eIF4G [7] and PABP [8,9] are proteolytically degraded. The absence of a 5′ terminal cap structure and cleavage of translation initiation factors prevents formation of a circularized template. The position and predicted secondary structure of the IRES element is outlined. C. Decline of host-cell protein synthesis and emerging viral translation in poliovirus-infected HeLa cells. Pulse-chase metabolic labeling of infected HeLa cells with [S35]methionine. By 2.5 to 3 hours postinfection, 2Apro-mediated degradation of eIF4G and PABP result in gradual shut-off of host translation. In parallel, IRES-mediated translation of viral gene products eclipses cellular cap-dependent translation already by 4 hours postinfection. The individual viral gene products released by proteolytic processing of the polyprotein are indicated.


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of poly(A) and the initiation complex stimulates translation, possibly by favoring 3′ to 5′ shunting of ribosomes [13]. Cleavage of eIF4G and PABP selectively inhibits cap-dependent cellular translation without impairing cap-independent viral protein synthesis mediated by the viral IRES (Figure 2C). As a result, host-cell protein synthesis dramatically declines as early as 2 to 3 hours postinfection (p.i.) while IRESmediated translation usurps the cellular protein synthesis machinery (Figure 2C). The IRES drives expression of a single large polyprotein proteolytically processed by virus-encoded proteinases to yield four structural and seven nonstructural gene products. Using viral genomic RNA as a template, the newly synthesized viral RNA-dependent RNA polymerase produces negative-strand intermediates that serve as templates for the synthesis of plusstrand RNA. Encapsidation of plus-strand RNA copies yields virus progeny (Figure 1). The poliovirus life cycle is highly productive and results in the release of infectious progeny through lytic destruction of the host cell. Poliovirus infection interferes with cellular function at multiple levels and induces profound and lethal disruption of host-cell biology. Shut-off of host-cell protein synthesis, cleavage of eukaryotic translation and transcription factors, disruption of intracellular vesicular traffic, disturbance of exonuclear transport, expression of cytotoxic viral gene products (e.g., the viral proteinase 2Apro), and overwhelming virus particle reproduction ultimately result in lytic destruction of the host cell. The lethal effects of poliovirus gene expression on the host cell occur early (2 to 4 hours p.i.) and are irreversible. In contrast to many other oncolytic virus candidates, the poliovirus life cycle and its lethal effects are cell-cycle independent. Poliovirus Pathogenesis Poliovirus infection occurs through fecal–oral transmission and results in primary replication within the gastrointestinal tract [14]. Gastrointestinal infection generally remains asymptomatic, but 1% to 2% of infected individuals develop neurological symptoms. Poliovirus pathogenicity is strictly

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limited to the primate CNS, where selective viral tropism for anterior horn spinal cord motor neurons produces a highly characteristic neurological syndrome dominated by flaccid paralysis (14; Figure 3). Despite major research efforts for almost a century, the critical determinants of poliovirus neuropathogenesis are incompletely understood. Because the inherent neuropathogenic properties of poliovirus may affect its clinical use as an oncolytic agent, continuing efforts will be required to elucidate the molecular mechanisms determining poliovirus neuroinvasion and its peculiarly restricted tropism for anterior horn motor neurons. Enteroviruses face severe obstacles on their route from the primary site of replication in the gut to the spinal cord. Central nervous system invasion may require viremia and blood-borne seeding to the CNS across the blood–brain barrier [14]. Alternatively, peripheral nerves may serve as a portal of entry for poliovirus invasion of the CNS. A variety of potential invasion routes have been demonstrated to be operational in experimental animals; e.g., direct penetration of the blood–brain barrier [15] or retrograde axonal transport [16,17]. Although the mechanism of poliovirus neuroinvasion remains under debate, available data clearly suggest that this process is highly inefficient. The low proportion of neurological

Figure 3 Histopathology of paralytic poliomyelitis in poliovirusinfected mice transgenic for the poliovirus receptor CD155. A. The normal murine lumbar spinal cord. B. Poliovirus infection results in selective destruction of anterior horn motor neurons (arrowhead).


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syndromes among individuals infected with poliovirus (⬃1% to 2%) is believed to reflect the difficulty for the virus to reach and invade the CNS. These observations indicate that peripheral administration of poliovirus-based oncolytic agents may not be suitable for efficient targeting of intracerebral malignant lesions (discussed below). The reason for the peculiar predilection of poliovirus for a highly specialized and minute population of CNS neurons has been a contentious issue since the first description of polio histopathology. The destruction of motor neurons is the result of direct targeting of these cells by poliovirus, rather than a bystander effect of infectious or inflammatory processes in their vicinity (as had been suggested in early reports; discussed in Ref. 18). However, the molecular mechanisms that constitute the basis for poliovirus specificity for motor neurons are not entirely clear. Virus susceptibility may be exclusively controlled by the expression patterns of cell surface receptors, or by the combined effect of cell external (e.g., receptors) as well as internal (e.g., host replication factors) determinants. For poliovirus, evidence for both cell-external as well as -internal determinants of host-cell specificity exists (discussed below). Poliovirus infection induces an acute neurological syndrome that may vary in extent from minor monopareses to fatal paralysis. Generally, the virus is unable to persist or induce chronic infection or latency. Most infected individuals clear the virus several weeks after infection and cease to shed infectious particles with their stool. It has become apparent, recently, that persistent enteric infection can occur in patients with inherent or acquired immunodeficiency [19]. Available evidence suggests that a depressed immune system may fail to clear the virus and permit prolonged enteric replication. ONCOLYTIC AGENTS BASED ON POLIOVIRUS Viral Target Tropism Targeting of oncolytic viral agents to tumor cells may be the most obvious and basic requirement to achieve oncolytic activ-

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ity. Target tropism of oncolytic viruses is determined by interaction of the virus particle surface with specific receptors expressed on the host-cell surface. This is followed by particle uptake and uncoating that will lead to the delivery of the viral genome into the host cell. Empirical results from clinical investigations of oncolytic viruses have suggested tumor cell targeting and virus spread as one of the main obstacles to achieve efficient oncolysis in vivo (discussed below). It therefore is imperative, prior to clinical application of oncolytic viruses, to determine the conditions for effective tumor cell targeting and to clarify expression patterns of their cellular receptor(s) in the target tumor type. Expression analysis of viral receptors in tumors is hindered by the fact that established tumor cell lines, the mainstay of pre-clinical investigations of oncolytic agents in tissue culture and xenotransplantation models, are poor representations of actual tumor tissue. Expression patterns of molecular determinants of virus attachment and entry in tissue culture cell lines commonly do not correspond to those observed in actual tumors. Consequently, experimental data of viral oncolysis in cultured tumor cell lines may yield results that poorly relate to the oncolytic effects in heterogeneous tumors. These difficulties demonstrate the need for more thorough investigation of the determinants for virus host-cell attachment, entry, and tissue invasion; their relationship with cancer; and their role in viral oncolysis. This fact has become evident with oncolytic adenoviruses, which use the IGSF member coxsackievirus/adenovirus receptor (CAR) for cell entry [20,21]. Oncolytic adenoviruses were applied therapeutically in clinical trials against malignant glioma prior to analysis of CAR expression profiles in actual tumors [22]. Recent investigations demonstrated that CAR expression levels in glioma cell lines selected for exquisite adenovirus sensitivity for pre-clinical investigations did not correspond to expression levels in patients’ tumors [23–26]. Given the cardinal importance of virus-receptor expression for tumor targeting and oncolytic activity, we have undertaken considerable efforts to elucidate the role of the poliovirus receptor CD155 in the pathogenesis of poliomyelitis and its


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potential role as a mediator of poliovirus tropism for malignant cell types. To this end, we have focused on the assessment of transcriptional regulation and expression patterns of the CD155 gene in the normal human CNS and in cancer. Detection of CD155 in the adult human CNS has been notoriously difficult because of exceedingly low expression levels in neural tissues and even in cell lines commonly used for poliovirus propagation (e.g., HeLa cervical carcinoma cells; 27). Structural similarities with insect members of the IGSF expressed during larval neurogenesis [28] suggested that CD155 expression may occur primarily during embryonic development. Developmental Expression of the CD155 Gene CD155 is the founding member of the nectin subfamily of the IGSF, structurally characterized by a V-C2-C2 domain arrangement (Table 1). Four poliovirus receptor-related proteins (PRR1–4; recently renamed nectins 1–4) have been identified in humans [29–32]. Apart from their pathogenic roles as viral receptors, nectins have been reported to mediate homophilic cell adhesion [33,34] and, through interaction with afadin, form part of the E-cadherin system [35–37].

Table 1 Members of the Nectin Family of Genes Gene products

Gene

Species

CD155, PVR

Human

CD155 (PVR) (soluble)

CD111, PRR-1, NECTIN-1 CD112, PRR-2, NECTIN-2 PRR-3, NECTIN-3 PRR-4, NECTIN-4

Human

Nectin-1

Human

Nectin-2

Human Human

Nectin-3 Nectin-4

AGM 1, AGM 2

Simian

TAGE4

Murine

sCD155 (sPVR) TagE4

Associated function(s)

Reference

poliovirus binding _′′_ -herpesvirus binding homophilic adhesion afadin binding homophilic adhesion poliovirus binding tumor antigen

1

30, 38 29, 33 31 32 39 40

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Given that intense searches for CD155 homologues in non-primates did not produce any obvious candidates, we evaluated the developmental regulation of the CD155 gene in a transgenic context [28]. Transgenic mice expressing the entire CD155 gene develop a neurological syndrome upon poliovirus infection indistinguishable from primate poliomyelitis [41,42]. These findings suggested that upstream regulatory regions of the CD155 gene faithfully control expression in a transgenic context. We constructed transgenic mice that express the reporter gene ␤-galactosidase (lacZ) under control of CD155 upstream regulatory regions [28]. Analysis of offspring embryos revealed that the CD155 promoter is active during midgestation in a triad of CNS structures known to induce motor neuron differentiation and maturation (28; Figure 4). Localized expression of CD155 in the floor plate, notochord, and spinal cord anterior horn of the developing CNS may explain why poliovirus neuropathogenicity is limited to the motoneuronal system. Activity of the CD155 promoter diminished considerably toward par-

Figure 4 Embryonic reportergene expression in mice transgenic for ␤-galactosidase (lacZ) controlled by CD155 upstream regulatory regions. A. As shown in this E12.0 embryo, reporter gene expression in the spinal cord and brain peaked during midgestation. B. LacZ expression was limited to notochord (nc), floor plate (fp) and the anterior horn (ah) of the developing spinal cord. The horizontal section shown corresponds to the upper cervical portion of the spinal cord.


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tum, and reporter gene expression became undetectable as early as 16 days post conception [28]. Our observations of highly restricted CD155 promoter activity in the motoneuronal system implicate the poliovirus receptor as a major determinant of specific vulnerability to poliovirus infection. Furthermore, its temporo-spatial expression pattern suggests a physiological role in cell adhesion, migration, and axonal guidance during embryonic CNS morphogenesis [28]. Prepartal downregulation of expression of the CD155 gene may explain low expression rates in adult tissues. Transcriptional Regulation of the CD155 Gene After the developmental profile of CD155 promoter activity had been determined in reporter transgenic mice, subsequent cell culture studies focused on dissecting the cis-acting elements and trans-acting factors that determine the expression pattern observed in the developing CNS. A combination of deletion studies, DNaseI footprinting and linker scanning mutagenesis were used to identify a 280-base-pair core promoter fragment of the CD155 gene that harbored four functional cisacting elements (termed FPI-IV) and a region of multiple transcriptional start sites (43–46; Figure 5A). The CD155 core promoter identified by these studies possessed all the information needed to direct cell type-specific transcription of a reporter gene; therefore much effort was subsequently dedicated to the identification of the transcription factors that interacted with FPI-IV. FPI and FPII are both bound by the developmentally expressed protein AP-2, a transcription factor that has been described to participate in the regulation of gene expression in the developing lens, retinal ganglion cell layer, and neural tube [47,48]. The expression of AP-2 in the developing CNS partially overlaps temporally and spatially with that of CD155, suggesting that the AP-2 transcription factors may influence the CD155 expression profile during embryogenesis. FPIV is bound by the transcription factor (NRF-1) nuclear respiratory factor, a potent activator of the CD155 core promoter in vitro [45]. Interestingly, vertebrate NRF-1 related

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Figure 5 A. Genetic structure of the upstream region of the CD155 gene. Footprints (FP) I/II were identified to interact with AP-2; FPIV with NRF-1; and FPIII contains a putative GLI binding site. The lower panel shows a GLI binding site deletion variant of the CD155 core promoter. B. Transient transfection assays. HeLa cells were cotransfected with either a wild-type CD155 promoter-driven reporter construct or the ⌬GLI variant and the indicated expression vector. Both Sonic hedgehog and GLI transcription factors induced CD155 promoter-mediated reporter expression.

factors have been shown to regulate the expression of genes required for proper retinal development [49]. The CD155 promoter is active in the developing retina [28] suggesting that regulation of the CD155 core promoter by NRF-1 could play a role in directing promoter activity to this location. The secreted morphogen Sonic hedgehog (Shh) plays an essential role in patterning many structures during development, including the notochord and ventral CNS, the developing limb, lung, and foregut [50–52]. The most thoroughly characterized site of Shh action is the anterior neural tube, associated with notochord, floor plate, and the motoneuronal system [50]. Secreted Shh from the notochord induces development of the floor plate, which, in turn, becomes a source of Shh that patterns many ventral neuron types along the entire anterior–posterior axis of the developing CNS [50].


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Given the overlapping expression patterns of Shh and CD155 in the developing CNS (46; Figure 6), we tested whether CD155 expression was modulated by Shh signaling [46]. Interestingly, CD155 mRNA was induced when a neuroepithelial cell line was treated with Shh protein [46]. Further studies showed that transient overexpression of Shh activated reporter-gene expression driven by the CD155 core promoter (46; Figure 5B). Upregulation of reporter expression was dependent on an intact GLI binding site within the CD155 core promoter (46; Figure 5B). In accordance with their observed function as downstream effectors of the Shh signal [52,53], GLI proto-oncogene transcription factors (Gli1 and Gli3) were also potent activators of the CD155 core promoter (46; Figure 5B). The Shh-GLI pathway has been recognized to be actively involved in the oncogenesis of neuroectodermal tumors and skin cancers [54–57]. Transcriptional regulation of the CD155 gene through Shh-GLI signaling during embryonic CNS development therefore may also affect its expression in tumors.

Figure 6 Expression of the poliovirus receptor CD155 (A) and Sonic hedgehog (B) overlaps (C, merged signal from A and B) in the floor plate of the developing spinal cord of CD155 transgenic mouse embryos [46]. Nonspecific rabbit immunoglobulin G yielded no signal (D).

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Figure 7 Cytopathic changes after PVS-RIPO infection and combined antigen capture and Western blot analysis of CD155 expression in cell and tissue homogenates of primary explant glioma cell lines (B-G), established glioma cell lines (H, I), and primary explant normal brain cultures (J). Left panel: The incubation intervals following infection are indicated atop. A. Mock-infected DU0108 cells did not show signs of cytopathic change stemming from the infection procedure. B–G. Infection with PVS-RIPO uniformly produced prominent cytopathic effects and lysis of primary explant glioma cultures already 6 hours postinfection. Middle panel: All cultures were freeze-thawed after documentation of their morphology to determine the virus yield by plaque assay. Efficient virus propagation rates were observed in all primary explant glioma cultures in accordance with the observed progression of cytopathic changes (B–G). In contrast, viral propagation failed in normal brain explant cultures (H, I).


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Association of CD155 Expression with Neuroectodermal Malignancy Increasing evidence links ectopic expression of cell adhesion molecules (CAM) of the IGSF to cancer and malignant glioma in particular [58–61]. Immunoglobulin superfamily-CAMs have been implicated in tumor progression [62,63], invasion, and metastasis [62,64,65] and have become prominent targets for anti-neoplastic therapy. Most oncolytic viruses in clinical trials against malignant glioma target IGSF-CAM receptors—adenoviruses through their affinity for CAR [20,21]; herpesviruses through their affinity for PRR-1 (nectin-1; 38). Four observations prompted us to evaluate the association of the IGSF member CD155 with neuroectodermal malignancy: (1) Other members of the nectin family are known tumor antigens (e.g., TagE4) (40; Table 1). (2) A large number of IGSF family members with structures or developmental expression patterns related to CD155 are ectopically expressed in cancer [62]. (3) Analyses of transcriptional regulation of the CD155 gene revealed that the morphogenic factor Shh and its downstream effectors, transcription factors of the gli family, potently activate CD155 transcription and protein expression [46]. (4) All established malignant glioma cell lines tested exhibit high levels of susceptibility to poliovirus. Given the known discrepancies of cell-surface-marker expression of established glioma cell lines and tumors occurring in patients, we focused our analyses on patient material and primary explant cultures derived therefrom. We analyzed six cases of glioblastoma multiforme (GBM) for their association with CD155 (27; Figure 7). Tumor biopsy material was obtained at the time of surgery and subjected to further analy䉳 Right panel: A–J. The amount of total protein analyzed is indicated atop.Antigen capture/Western blot assays of cell and tissue homogenates are labeled ‘‘C’’ and ‘‘T’’, respectively.The case origin of the homogenate is indicated on the left. HTB-14 and DU54 are widely used established glioma cell lines.Tissue homogenates of lumbar spinal cord (LSC) and temporal cortex (TC) were analyzed in parallel to lysatesproduced from tumor tissues.

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sis of virus susceptibility and CD155 expression levels. In accordance with universal upregulation of CD155 gene expression in established glioma cell lines [27,83], CD155 was detected in all GBM biopsy specimens (Figure 7). Subcultivation of tumor tissue obtained from patients did not alter receptor expression, given that Western blot analysis revealed parallel amounts in tumor tissue and primary explant cultures (27; Figure 7). CD155 expression in the normal human brain, including the spinal cord, is exceedingly low (27; Figure 7). In accordance with our receptor expression data, susceptibility to PVS-RIPO was universal among the panel of GBM primary cell lines (Figure 7). The proposal to consider PVS-RIPO for use as an oncolytic agent is not based on properties of the virus alone, but motivated mainly by natural target tropism for malignant glioma cells mediated by ectopic expression of CD155. Our pre-clinical evaluations strongly suggest that, at least in high-grade malignant glioma, universal receptor expression leads to exquisite sensitivity to the oncolytic effects of PVS-RIPO infection. Most importantly, our empirical results are not based on studies of established glioma cell lines but rather on patients’ tumor material. Studies of poliovirus susceptibility suggest that CD155 expression may also occur in non-CNS malignancies. Accordingly, an association of CD155 with colorectal cancer has recently been reported [66]. Physiological Functions of CD155 CD155 was identified because of its role as a cellular poliovirus receptor [1]. To date, apart from hypothetical functions suggested by its predicted structure, its relation to other members of the IGSF, or its expression pattern during CNS embryogenesis, CD155 has not been implicated functionally in any physiological process. Because it is likely that CD155 exerts its physiological function(s) through interaction with specific ligands, experimental approaches have focused on the identification of CD155 binding partners. Recently, a search for a physiological binding partner for CD155 has identified the extracellular matrix (ECM) protein


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vitronectin [67]. Although vitronectin is widely distributed in a number of organs, its presence coincides with known sites of CD155 expression—e.g., the floor plate of the developing neuraxis and retina [28,67,68,69]. Moreover, vitronectin has been implicated in motor neuron induction and differentiation [69,70]. Most significantly, vitronectin is the major ECM component in malignant gliomas and is particularly abundant in high-grade malignant gliomas, where it has been reported to promote glioma cell survival and invasion [70,71]. In general, IGSF-CAMs are believed to confer invasive properties to cancer cells through their interactions with ECM proteins [62]. CD155 affinity for vitronectin establishes a further link between IGSF-CAMs and the ECM in malignant glioma. Because local invasion is a standard feature of malignant glioma, posing severe limits on surgical and radiological treatment regimens, the functional significance of IGSF-CAM expression in malignant glioma has been under intense investigation. The physiological significance of CD155–vitronectin interactions in the developing CNS and in malignant CNS tumors remains to be evaluated. Tumor-Specific Virulence Once the viral genome has reached the interior of the host tumor cell, oncolytic activity depends on the virus’ ability to replicate and induce cytopathic changes and tumor cell killing. To render oncolytic viruses clinically applicable, viral replication and cytopathogenicity need to be selective, killing off tumor cells while sparing healthy cells. Thus, pathogenic viruses considered for use as oncolytic agents—e.g., poliovirus—need to be manipulated to prevent virus propagation and associated toxicity in nonmalignant tissues without affecting growth in transformed cells. This property has been termed a conditional replication phenotype [73–75]. A number of mechanisms have been targeted to achieve conditional virus replication in cancerous cells. These include deletion of endogenous viral genes coding for products required for replication in nonmalignant cell types but expendable in tumor cells, and insertion of tumor-specific transcrip-

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tional control elements into the viral genome, promoting viral gene expression selectively in cancer cells. Despite its inherent ability to infect and destroy cancer cells, poliovirus’ neuropathogenic properties prevent its use as an oncolytic agent. Because poliovirus pathogenicity is limited to infection of spinal cord and brain stem motor neurons, a conditional replication phenotype in tumor cells would be achieved by eliminating the virus’ ability to propagate in neuronal cell types. In contrast to large DNA viruses under consideration for use as cancer therapeutics—e.g., adeno- and herpesviruses—poliovirus genomes are characterized by extreme genetic austerity (the poliovirus genome is ⬃7.5 kB in length, compared with ⬃150 kB for ␣-herpesviruses; 76). To adapt to the extraordinarily high mutation rate of their replication machinery, picornaviruses have limited the size of their genome and number of their gene products to an essential minimum [76]. Therefore, any manipulations to delete viral coding sequences or add extraneous regulatory sequences would either severely impair virus viability or trigger deletion events to remove foreign inserts. To confer a conditional replication phenotype to poliovirus, we manipulated the viral IRES element, which is critically involved in translation control of the poliovirus genome (discussed above). Our approach is the first to achieve a conditional replication phenotype through manipulation of non-coding sequences regulating translation and is the first treatment targeting tumor cells at the level of translation control. Swapping the Poliovirus Internal Ribosomal Entry Site Element Poliovirus has demonstrated a surprising level of flexibility with regard to accommodating heterologous IRES elements of variable origin within its genome. Insertion of closely related enteroviral IRESes (e.g. Coxsackievirus B4, Coxsackievirus A9, or Enterovirus 71; M. Gromeier et al, unpublished observations), more distantly related cardioviral IRESes (e.g., encephalomyocarditis virus) [77] or even the unrelated hepatitis C


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virus IRES [78] produces viable polioviruses with wild-type growth properties. Furthermore, these chimeric polioviruses maintained their pathogenic potential and caused paralytic poliomyelitis in CD155 transgenic mice [79]. The most remarkable effect of IRES exchange was observed with a chimeric poliovirus, termed PVS-RIPO, carrying the IRES element of human rhinovirus type 2 (HRV2), a fellow picornavirus of the rhinovirus genus (79; Figure 8). The chimeric PVS-RIPO, while replicating with wild-type kinetics in HeLa cells, had acquired a dramatic reduction of neuropathogenicity (79; Figure 8). This recombinant was unable to replicate within the spinal cord of CD155 transgenic mice (Figure 8) and failed to cause poliomyelitis in these animals, even after intracerebral administration of doses exceeding the wild-type LD50 by seven orders of magnitude [79]. Accordingly, polioviruses containing the HRV2 IRES element failed to induce spinal cord pathology and neurological disease after intraspinal inoculation in Cynomolgus macaques (80; Table 2). Rhinoviruses cause the common cold and do not exhibit tropism for neuronal tissues. During infection, rhinovirus rep-

Figure 8 The cell type-specific replication deficit of PVS-RIPO. Genetic structure (left panel), replication profile in DU54 glioblastoma (blue diamonds) and Sk-N-Mc neuroblastoma (red squares) (left middle panel), replication in the spinal cord of CD155 transgenic mice (right middle panel), and LD50 in CD155 transgenic mice (right panel) of wild-type poliovirus (A) and PVS-RIPO (B). The HRV2 IRES is outlined in red.

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Table 2 Monkey Neurovirulence Testing Results Virus PV1(MAHONEY)* NA-4** PV1(RIPO) PVS-RIPO¶

No. Cynomolgus macaques

Mean lesion score

4* 14 14 ND

2.48⫾0.34* 0.87⫾0.38 0.92⫾0.42 ND

Clinical outcome 75% fatal* No clinical symptoms No clinical symptoms

* The data shown on wild-type PV1(Mahoney) are derived from a separate study (103). **NA-4 is a reference PV1(S) strain. NA-4 and PV1(RIPO) were studied in parallel by K. Chumakov (U. S. Food and Drug Administration, Center for Biologics Evaluation and Research). †¶PVS-RIPO is scheduled to undergo primate testing at the same facility in the near future.

lication is restricted to the upper respiratory tract. Thus, neuronal dysfunction of its IRES element would not affect rhinovirus pathogenicity. The nonpathogenic phenotype of PVS-RIPO corresponded to a pronounced defect of this virus to propagate in cultured cell lines of neuronal origin,—e.g., Sk-N-Mc neuroblastoma cells (79; Figure 8). Neuroblastoma cell lines, albeit their malignant origin, have served as a convenient tissue culture model to study poliovirus replication in a neuronal environment [81,82]. Remarkably, despite a major impediment to virus replication in neuronal cell types, PVS-RIPO retained wild-type growth kinetics and superb oncolytic potential for malignant glioma cell lines—both established cell lines [83] and primary explant cultures (27; Figures 7 and Figures 8). Our observations suggested that insertion of a heterologous HRV2 IRES into the poliovirus genome suppressed neuronal replication and, hence, pathogenesis. Because IRES-mediated selective replication deficits provide the basic rationale to use polioviruses as oncolytic agents, we intend to unravel the molecular mechanisms responsible for the observed phenotype. The Genetic Basis for the Tumor-Specific Replication Phenotype To elucidate the molecular mechanism for tumor-specific function of the HRV2 IRES element, we are pursuing genetic and


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biochemical approaches—identifying the genetic locus for the non-neuropathogenic phenotype of PVS-RIPO and characterizing the interaction of the IRES with the cytoplasmic milieu of glioma vs. normal neuronal cells. Following the simplest strategy of genetic analyses of poliovirus, we carried out adaptation experiments of PVS-RIPO to identify genetic alterations that might restore the neurovirulent phenotype upon serial passages in neuronal cell lines or CNS tissues. Interestingly, passage in Sk-N-Mc neuroblastoma cells or in CD155 transgenic mice did not produce any neurovirulent revertants [83]. This finding indicated a high degree of genetic stability of the nonpathogenic phenotype of PVS-RIPO (a desirable safety feature for oncolytic viruses; discussed below), which prevented isolation and characterization of neurovirulent revertants. We therefore are limited to reverse genetics to delineate the genetic basis of PVS-RIPO neuro-attenuation. Because of the high level of conservation of the predicted secondary structure of the HRV2 and poliovirus IRESes, individual stem-loop structures of either IRES element can be recombined without affecting the ability of the virus to grow in malignant glioma cells [80]. We used such a ‘‘mix-and-match’’ recombination strategy to determine the genetic locus for neuronal IRES defects (80; Figure 9). Our experiments implicated IRES domains V/VI, in the neurovirulent phenotype (80; Figure 9). Insertion of HRV2 IRES domains V/VI was sufficient to reduce neurovirulence in CD155 transgenic mice to the level of PVS-RIPO (80; Figure 9). Conversely, HRV2 IRES domains V/VI alone conferred attenuation of neurovirulence to poliovirus (80; Figure 9). Our findings implicating IRES domains V/VI in the neurovirulent phenotype of poliovirus are in accordance with a proposed role of the IRES in attenuation of the live attenuated vaccine strains of poliovirus (the Sabin strains). All three Sabin serotypes feature point mutations within a confined region of IRES domain V that have been implicated in the attenuation phenotype [14]. Sequence differences mapping to IRES domain V have been proposed to cause functional deficits through their effect

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Figure 9 The genetic locus for neuronal internal ribosomal entry site (IRES) function. Poliovirus (A), PVS-RIPO (B), and mix-andmatch IRES hybrids (C, D) were tested for their neuropathogenic potential in CD155 transgenic mice. *No neurological symptoms were observed after administration of 109 plaque forming units.

on the predicted secondary structure of the IRES element [84,85]. This notion is reinforced by serial passaging experiments of poliovirus type 1 (Sabin) in cultured neuronal cells. These experiments yielded neurovirulent variants in which base pairing and, hence, stem loop stability were restored to correspond to the wild-type structure [86]. The evaluation of the influence of predicted secondary structure on HRV2 IRES function in neuronal vs. malignant glioma cells is in progress. Apart from cis effects of IRES structure on cell type-specific function, trans-acting factors supplied by the infected host cell have been proposed as a major determinant of IRES function and its cell type-specific restrictions. Cellular trans-Acting Factors The mechanism of translation initiation at the IRES is fundamentally different from that of eukaryotic mRNAs (discussed


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above, Figure 2). Like the latter, translation mediated by internal ribosomal entry appears to depend on canonical translation initiation factors required for ribosomal scanning, with the exception of the cap-binding initiation factor eIF4E [87]. In addition, noncanonical trans-activating eukaryotic factors may be needed for efficient IRES function. A number of trans-activating factors have been suggested to interact with picornavirus IRESes. These include the polypyrimidine tract binding protein (PTB) [88], the La autoantigen (the target for autoantibodies in systemic lupus erythematosus) [89], the poly(rC) binding protein 2 (PCBP2) [90,91], and the RNA chaperone ‘upstream of N-ras’ (unr) [92]. The identification of trans-acting factors followed procedures tracking polypeptide binding to IRES sequences. Isolation of factors that bind to IRES sequences does not necessarily imply this binding activity to be functionally significant. Recently, we have provided the first evidence for PTB to be functionally required for poliovirus replication in vivo [93]. The requirements for IRES function appear to differ individually, meaning that distinct IRESes require different sets of interacting trans-activating factors. Polypyrimidine tract binding protein may stimulate all picornavirus IRESes—e.g., cardioviruses [94], aphthoviruses [95], enteroviruses [88], rhinoviruses [92], and hepatoviruses [96]—and has been reported to trans-activate the IRES of HCV [97] and to bind even to putative eukaryotic IRESes [98]. In contrast, requirement for unr seems, at this point, to be limited to the IRESes of polioand rhinoviruses [92,99]. The role of cellular noncanonical trans activities in IRES translation suggests that IRES function and, thus, pathogenic properties, could co-vary with the set of stimulating factors available in the infected cell. For example, neuron-specific deficits of the HRV2 IRES could be a reflection of the differences of the cytoplasmic make-up of neuronal vs. glioma cells. Such a scenario has been proposed to be a determinant of the neuropathogenic properties of another picornavirus, Theiler’s murine encephalitis virus [100]. We are investigating a number of candidate eukaryotic RNA-binding proteins with affinity for the HRV2 IRES and

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their role in the conditional replication phenotype of PVSRIPO. All investigations of the interaction of eukaryotic IRES trans activities were based on the premise that IRES activity is determined by the availability of activating factors alone. Our experimental results strongly suggest that not only is IRES function subject to the presence of stimulating factors, but repression of IRES function can occur through IRES-binding proteins with inhibitory function (M. Merrill et al, unpublished results). PVS-RIPO as an Oncolytic Agent Inherent tropism for CD155, a tumor antigen ectopically expressed in neuroectodermal malignancy, and a nonpathogenic profile in primates, raise the possibility of using PVS-RIPO as an oncolytic agent. We have carried out extensive studies in animal xenotransplantation models to characterize the oncolytic potential of PVS-RIPO in vivo. Treatment of athymic mice harboring subcutaneous glioma xenografts with PVS-RIPO resulted in dramatic tumor regression and, eventually, elimination (83; Figure 10). Intratumoral virus replication corresponded with gradual shrinkage of the xenograft, indicating that virus propagation within tumor cells reduced the xenotransplant (Figure 10B). Similar results were obtained after i.v. or intramuscular administration of PVS-RIPO [83]. Treatment of athymic mice carrying bilateral xenografts by intratumoral inoculation of PVS-RIPO produced shrinkage of the contralateral mass, indicating efficient targeting of tumor cells by the agent [83]. Histopathological evaluation of the diminishing xenografts revealed intense infiltration of the neoplastic lesion followed by replacement with fibrous scar tissue (Figure 10A). Intratumoral inoculation of PVS-RIPO into intracerebral glioma xenografts similarly produced tumor regression (Figure 11A). However, peripheral forms of administration of the virus had little effect on tumor progress and survival (Figure 11B). These observations confirm the notion of inefficient CNS invasion of circulating poliovirus (discussed above) and exclude the possibility of treating intracerebral neoplastic processes via peripheral administration of PVS-RIPO.


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Figure 10 Treatment of subcutaneous glioma xenografts with PVS-RIPO. A. Subcutaneous HTB15 glioma xenotransplants (Day 0 ⳱ 10 mm diameter) were treated with a single intratumoral inoculation of PVS-RIPO. Seven days after virus treatment, the viable tumor had shrunk considerably. Approximately 90% of the tumor mass had been destroyed and replaced by fibrous scar tissue. The detail images (right panel) show the remaining tumor nodus surrounded by infiltrating cells and scar tissue. At day 14 after treatment, only a minuscule remnant of tumor can be distinguished (arrowhead in the detail image). At this time, the scar had replaced almost the entire tumor mass. B. The kinetics of tumor regression in PVS-RIPO–treated xenografted animals (blue bars) and their untreated peers (red bars). Tumor regresson corresponded to the kinetics of intratumoral virus propagation (black diamonds).

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Figure 11 Treatment of intracerebral glioma xenografts with PVSRIPO. A. Tumor regression and elimination after intratumoral inoculation of PVS-RIPO into intracerebral HTB14 glioma xenotransplants [83]. The lower panel shows the tumor implantation site in detail. The injection locale is indicated by arrowheads. B. Survival of athymic mice harboring intracerebral HTB14 xenotransplants after mock treatment (dark blue diamonds), intramuscular (green diamonds), intravenous (red diamonds), and intratumoral (light blue diamonds) administration of PVS-RIPO. Virus treatment was implemented at day 12 after xenografting.

Further evaluations of the microdiffusion of PVS-RIPO from the site of inoculation and the evaluation of alternative forms of intratumoral administration (stereotactic bolus injection vs. convection-enhanced delivery) are in progress. SAFETY Attenuation of Neuropathogenic Properties The most imminent and serious safety concern associated with therapeutic use of polioviruses is their neuropathogenic potential. We have identified a powerful new way to achieve superb levels of poliovirus neuroattenuation without affecting growth in malignant glioma cell types. Insertion of a heterologous


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HRV2 IRES into the poliovirus genome drastically reduced the virus’ ability to propagate in cells of neuronal origin and eliminated neuropathogenicity in a transgenic mouse model for poliomyelitis and in Cynomolgus macaques [80]. The phenomenon of poliovirus neurovirulence and its attenuation has been the subject of numerous investigations ever since epidemic paralytic poliomyelitis emerged as a public health concern. The first thoroughly characterized attenuated poliovirus strains were generated by A. Sabin through serial passaging of wild-type neurovirulent polioviruses in a variety of host cell types [101]. Sequencing of the poliovirus serotype 1 (S) [PV1(S)] genome in 1981 [102] and comparison with the sequence of its wild-type progenitor [103] provided the first glimpse into molecular mechanisms of the attenuation of poliovirus neurovirulence. Analysis of the molecular basis for attenuation of the Sabin vaccine strains of poliovirus has implicated major attenuating determinants within the capsid as well as point mutations within stem loop domain V of the IRES (discussed above; 14). The coding regions for the capsid proteins of the Sabin vaccine strains, compared with their wild-type progenitors, contain mutations (encoding 11 amino acid exchanges in serotype 1 and 3 in serotype 3; serotype 2 is a naturally occurring attenuated variant neurovirulent progenitor of which is unknown). Furthermore, reversions to the neurovirulent phenotype in vaccinees are commonly accompanied by reversion to the wild-type capsid or IRES sequences [14,76]. Because the attenuating effects of the Sabin capsids are well documented, we opted to construct a prototype oncolytic poliovirus in a PV1(S) background. PV1(S) is considered to have the highest level of neuroattenuation because it features the largest number of capsid mutations associated with attenuated neurovirulence. This consideration is supported by the fact that reversion to neurovirulence in immunized children is far more common with the type 2 and 3 (S) strains than PV1(S) [14,76]. Preliminary investigation of poliovirus/rhinovirus chimeras in monkey neurovirulence assays demonstrated that insertion of the HRV2 IRES alone, yielding PV1(RIPO), re-

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duced poliovirus neurovirulence to the level of PV1(S) (Table 2). It is reasonable to assume that combination of the HRV2 IRES and the coding region of PV1(S) containing the major attenuation determinants mapping to the capsid will further reduce neurovirulence of PVS-RIPO in primates. Prior to clinical application, the oncolytic PVS-RIPO will be submitted to comprehensive neurovirulence evaluation after intraspinal and intrathalamic inoculation in Cynomolgus macaques following standard World Health Organization procedures. Genetic Stability and Spontaneous Reversion to Neurovirulence The live attenuated Sabin vaccine strains are known to spontaneously revert to a neurovirulent phenotype. This event has been reported to occur upon prolonged passage in tissue culture, in the gastrointestinal tract of vaccinees without clinical signs of paralytic polio, and in cases of vaccine-associated poliomyelitis [14,104]. Despite this tendency, vaccine-related incidences of paralytic poliomyelitis are extremely rare (2 to 3 cases per million vaccinated). The inherent genetic variability of polioviruses is cause for the concern that genetic manipulations carried out to achieve attenuation of neurovirulence may revert upon virus replication in vivo. In contrast to the Sabin vaccine strains, which are attenuated by a series of point mutations scattered throughout the genome (e.g., only four nucleotide substitutions for serotype 3), PVS-RIPO contains an entire genetic element (the IRES) with severe functional deficits in neuronal cells. Serial passaging of PVS-RIPO in Sk-N-Mc neuroblastoma cells or CD155 transgenic mice failed to produce neurovirulent revertants (discussed above; 83), indicating that the genetic basis for attenuation of PVS-RIPO must be comparatively broad. Our current insight suggests that the neuronal deficit of the HRV2 IRES rests on structural features determined by complex sequence elements (stem loop domains V/ VI) rather than single nucleotide exchanges, as has been proposed for the Sabin strains [14].


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Neurovirulence per se is not an indicator of poliovirus fitness or replication potential. Therefore, to explain the occurrence of adaptation events with the Sabin strains, the question arises how reversion to neurovirulence benefits their growth rate. Notably, reversion to neurovirulence of the Sabin vaccine strains commonly occurs in non-neuronal cell types—e.g., VERO cells [105] or the human gut [106]. Because the Sabin strains are characterized by reduced growth compared with their wild-type progenitors in many cell lines—e.g. VERO monkey kidney, HeLa adenocarcinoma, DU54 glioma—adaptation events may simply restore optimal replication rates. This would mean that reversion to neurovirulence is a side effect of adaptation to optimal growth rates. Despite its superior attenuation profile, PVS-RIPO, in contrast to the Sabin strains, grows with wild-type kinetics in all permissive cell lines [79,83]. Prolonged passaging of PVSRIPO in VERO, HeLa, or DU54 cells and even neuronal cell types did not alter the PVS-RIPO genotype (Dobrikovaey et al., unpublished observations). Our observations may indicate that the observed genetic stability of PVS-RIPO is a reflection of unimpeded growth in permissive cell lines and the broad genetic basis of its neuron-specific replication defect. Intergenomic Recombination It is well established that during picornavirus replication, extensive intergenomic recombination can occur. These events have been observed in tissue culture systems [76] and in cellfree poliovirus replication systems [107], as well as in vivo [108]. Although there is substantial evidence for intergenomic recombination among strains of the same species (e.g., among the three live attenuated vaccine strains of poliovirus) [108], the occurrence of recombination events involving different enterovirus species has never been documented. Given the extensive sequence homology among enteroviruses [14], intergenomic recombination events involving multiple enterovirus species are conceivable. The propensity for intergenomic recombination entails the possibility that genetically engineered attenuated poliovi-

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rus strains may acquire pathogenic properties through recombination with other poliovirus strains or non-polio enteroviruses. Because it is highly improbable that cancer patients may harbor active poliovirus infection (only patients with documented anti-poliovirus immunization will be enrolled in clinical trials), recombination events involving circulating wildtype or live attenuated poliovirus strains are unlikely to occur. This leaves the possibility of recombination with non-polio enteroviruses in patients harboring concomitant enterovirus infections at the time of oncolytic virus treatment. Using established tissue culture and cell-free replication systems, we have analyzed the frequency of recombination events involving PVS-RIPO and non-polio enteroviruses. Because of their very close genetic kinship to poliovirus [109], our experiments have focused on ‘C’ cluster Coxsackie A viruses (CAV17, 21, and 24). Experimental conditions that favored the occurrence of recombination events involving different poliovirus strains failed to produce recombinant hybrid genomes containing CAV sequences. Our tissue culture experiments clearly demonstrate that intergenomic recombination events involving polio- and non-polio enteroviruses are very unlikely to occur. However, we cannot exclude the possibility that specific conditions prevailing in the human gastrointestinal tract or CNS may favor recombination events that fail to materialize in vitro. REFERENCES 1. Mendelsohn CL, Wimmer E, Racaniello VR. Cellular receptor for poliovirus: molecular cloning, nucleotide sequence, and expression of a new member of the immunoglobulin superfamily Cell 1989; 56:855–865. 2. He Y, Bowman VD, Mueller S, Bator CM, Bella J, Peng X, Baker TS, Wimmer E, Kuhn RJ, Rossmann MG. Interaction of the poliovirus receptor with poliovirus Proc Natl Acad Sci U S A 2000; 97:79–84. 3. Nomoto A, Lee YF, Wimmer E. The 5′ end of poliovirus mRNA is not capped with m7G(5′)ppp(5′)Np Proc Natl Acad Sci U S A 1976; 73:375–380.


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13 Oncolytic Viruses that Depend on Loss of RB or p53 FRANK MCCORMICK University of California-San Francisco Cancer Research Institute San Francisco, CA

INTRODUCTION Loss of the RB checkpoint is a fundamental step in the development of cancer [1,2]. Loss may occur through direct inactivation of the RB gene itself, or through hyperactivation of CDK4, causing inactivation of RB through uncontrolled phosphorylation. In many human cancers, the HPV protein E6 inactivates RB directly. One way or another, tumor cells lose RB function and upregulate activity of the transcription factor complex referred to as E2F [3] (Figure 1; 4). This allows unscheduled entry into S-phase, and suppression of differentiation and se781

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nescence, because E2F directs transcription of genes involved directly in replicating DNA and synthesizing pools of DNA precursors. Dihydrofolate reductase and thymidylate synthase, for example, are targets of E2F activity, along with cyclins A and E, MCM proteins, and many other key regulators of S-phase (Figure 2). Another consequence of E2F activation through loss of RB is induction of p14ARF, an inhibitor of MDM2 (Figure 1). In the absence of MDM2 activity, p53 accumulates and can turn on target genes involved in growth suppression or apoptosis. To tolerate high levels of E2F, tumor cells must therefore suppress p53 activity. This is achieved through mutation of p53 itself, through suppression of p14ARF expression via promoter methylation or mutation, or through increased MDM2 activity. Expression of HPV E6 is another way of degrading p53 that occurs in human tumors of squamous cell origin. In general terms, tumor cells can therefore be characterized as cells in which E2F is de-repressed and p53 is sup-

Figure 1

Oncolytic Viruses that Depend on Loss of RB or p53

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Figure 2

pressed. These cells are characterized by uncontrolled entry into S-phase and reduced susceptibility to apoptosis. High levels of E2F and low levels of p53 are conditions that are induced by infection of epithelial cells by adenoviruses. E1a binds RB and liberates E2F [5–9]. Products of these genes are used to synthesize viral DNA in infected cells. In addition, E2F transcribes the E2 region of the viral genome, a region that encodes viral DNA polymerase and DNA-binding proteins. This, of course, is where the name E2F comes from: a cellular factor that transcribes E2 in an E1a-dependent manner. Uncontrolled activation of E2F, however, provokes accumulation of p53, as described above. p53 could attenuate replication by causing apoptosis, or by other means. For example, p53 could, in principle, block entry into S-phase by induction of p21. However, E1a is known to overcome p21-induced arrest and, indeed, p21 is not induced significantly during infection. It is well established, however, that adenoviruses, like other DNA viruses, need to inactivate p53 to achieve efficient replication, although the precise reason for this has not been formally established [10]. Adenoviruses eliminate p53 by produc-

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tion of E1B 55k, which binds p53 directly and blocks its function [11–16], and by E4orf6, which forms a complex with E1B 55k and p53, promoting p53 degradation [17–19]. Based on the remarkable parallel between molecular events that cause cancer and those involved in initiating virus replication, we have developed adenoviruses that replicate selectively in cancer cells. Specificity is based on the following hypotheses: (1) Viruses that lack E1a are defective for replication in normal cells, because RB blocks replication, and are permissive in cancer cells, in which RB is defective. (2) Viruses that lack E1B 55k are defective in normal cells because p53 blocks replication, but permissive in cancer cells that lack functional p53. Both of these hypotheses are based on the supposition that the sole function of E1a and E1B 55k relate to inhibition of RB and p53, respectively. Clearly, this is not the case, and we discuss below how the general concept embodied in the hypothesis has been translated into reality through analysis of other functions of these viral proteins. VIRUSES THAT DEPEND ON LOSS OF RB The interaction between E1a and RB was described in 1988, and set the stage for understanding how viral proteins transform cells. E1a mutants that fail to bind RB were identified [20], and it was realized that RB binding is one of many functions of E1a that contribute to transformation. In 1992, we speculated that an adenovirus encoding a mutant form of E1a that fails to bind RB should replicate efficiently in RB-deficient cells, but fail to grow in normal cells. One such mutant virus is dl922/947: It contains a deletion in the CR2 region of E1a that prevents interaction with RB and related proteins We expected that rapidly proliferating cells would be somewhat permissive for this mutant virus because normal cells inactivate RB during normal transition through the cell cycle. To our surprise, we found that even quiescent cells could, in fact, support replication by this mutant virus [21]. Proliferating cells, as expected, were more permissive and tumor cells, as expected, were fully permissive for replication.


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Replication of dl922/947 in primary cells must be attributable to alternative mechanisms for activating E2F. The E4 region expresses a protein referred to as E4orf6/7, the function of which is to bind to E2F and dimerize the transcription factor in an orientation that directs E2F activity to promoters with two head-to-tail E2F binding sites (Figure 3) [22–27]. The E2 region of the viral genome has such an orientation, as does the cellular promoter for E2F-1. Binding of E4orf6/7 to E2F can displace RB binding. We therefore speculated that leaky expression of E4orf6/7 in primary cells in culture can lead to E2F activation and thereby initiate entry into S-phase and activation of E2 transcription in the absence of E1a/RB complexes. We, therefore, constructed a virus in which the E4 region was placed under the control of E2F, so that E4 expression would be selective for tumor cells in which E2F levels are high. We also engineered E1a with a deletion in the RB binding site, under the E2F promoter. The resulting virus, ONYX-411, has the properties of being highly restricted for replication in normal cells, even while they proliferate, but being fully permissive for replication in tumor cells (Figure 4) [21]. Whereas ONYX-411 contains three elements of selectivity (E2F drives E1a, E1a is mutated for RB binding, and E2F

Figure 3

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Figure 4

drives E4), the simpler virus, which contains only an E1a deletion (dl922/947) for selectivity [28,29], has shown promise as a cancer-selective virus, and an improved version of this virus that includes an RGD motif to improve infectivity recently entered pre-clinical evaluation. (Fueyo et al, in press) ONYX-015 AND THE P53 PATHWAY ONYX-015 is dl1520, an adenovirus made by A. J. Berk and colleagues in 1987 [11]. This virus lacks the E1B 55K gene and is therefore unable to block p53. In 1992, we proposed that such a virus should replicate selectively in cancer cells, since these cells typically lack p53 and should therefore not need E1B 55K. In normal cells, p53 would block replication. ONYX015 [30] entered clinical trials for head and neck cancer in 1996 [31] and is still under clinical investigation. p53 is induced during infection of normal cells by adenoviruses, as a result of expression of E1a and activation of E2F. p14ARF is induced under these conditions, and MDM2 is inhibited, allowing p53 to accumulate as described above (Figure 1). Primary cells infected with ONYX-015 are indeed attenuated for replication, and p53 is induced to very high levels


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in these cells. Suppression of p53 by dominant negative p53 mutants increases ONYX-015 replication, showing that p53 is responsible, in part, for ONYX-015 attenuation. In tumor cells, replication of ONYX-015 varies tremendously relative to wild-type adenovirus. Originally, we thought that this might be because of different states of p53 activity in these cells. The most permissive cells we examined, cervical cancer C33a cells, replicated ONYX-015 at wild-type levels of efficiency. These cells harbor a mutation in p53 that renders the protein inactive. On the other hand, U2OS osteosarcoma cells, which express wild-type p53 activity, are severely attenuated for ONYX-015 replication. Later, it was shown by Zur Hausen and colleagues that attenuation of ONYX-015 in U2OS cells is unrelated to p53 function: They eliminated p53 activity using a dominant negative construct and failed to rescue ONYX-015 replication [32]. Likewise, we and others observed a lack of correlation between p53 status and ONYX015 replication [33–36]. Two issues needed to be addressed: First, how is ONYX015 able to replicate in tumor cells that retain wild-type p53? Second, why does ONYX-015 fail to replicate in some cancer cells in which p53 function is missing? Replication of ONYX-015 in Tumor Cells with Wild-Type p53 The first of these issues was quite easy to address. It was discovered in 1999 that tumor-derived cell lines that retain wild-type p53 lose expression of p14ARF. This protein connects E2F to p53, as shown in Figure 1. We, therefore, tested whether tumor cells retaining p53 support replication of ONYX-015 because they are defective for p53 function. Indeed, infection of such cells by ONYX-015 fails to activate p53. Forced expression of p14ARF induces high levels of p53 and blocks ONYX-015 replication in a p65-dependent manner. In such tumor cells, p53 can be activated by DNA damaging agents because these insults do not depend on p14ARF. This led to the misleading impression that tumor cells with wildtype p53 are normal with respect to the p53 pathway. We con-

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cluded that loss of p14ARF permits replication of ONYX-015 in tumor cells with wild-type p53 [37]. Failure of ONYX-015 to Replicate in p53Defective Tumor Cells E1B 55K has additional functions: Failure to replicate in p53defective cells must reflect ONYX-015’s requirement for these other functions in nonpermissive tumor cells such as U2OS. Equally, permissive cells, such as HCT116 colon cancer cells and C33a cells, must supply all functions of E1B 55K to allow replication of ONYX-015 at wild-type levels in these cells. Other functions of E1B 55K include export and translation of viral late mRNAs, shutoff host protein synthesis. The molecular basis of these functions and the relationship to one another are under investigation. A mutant form of E1B 55K that fails to bind p53 but retains other functions might seem to provide a solution to ONYX-015’s replication defect in certain cancer cells, while retaining attenuation in primary cells. Such a mutant has been constructed: Shen and workers characterized a panel of virus-containing point mutations in E1B 55K for replication in U2OS cells and for p53 binding [38]. Mutants were obtained that had the desired properties—specifically, mutants R240A and H260A failed to bind and degrade p53. The H260A of E1B 55k also failed to interact with E4orf6, whereas R240A remained wild-type in this function. R240A replicated efficiently in cancer cells in which ONYX-015 is defective. However, this mutant replicates quite efficiently in normal cells, despite induction of high levels of p53. This is because the mutant restores shutoff of host protein synthesis, in contrast to ONYX015. As a result, p53 that is induced early in infection cannot induce expression of target genes, which, of course, depend on host protein synthesis. It is therefore apparent that ONYX015’s attenuation of replication in normal cells depends on lack of both functions of E1B 55K—p53 binding and host shutoff. Replication in tumor cells depends on the degree to which tumor cells supply E1B 55K functions that are unrelated to p53.


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CLINICAL EXPERIENCE WITH ONYX-015 ONYX-015 entered clinical trials for head and neck cancer in 1996. Response rates of over 60% were reported in tumors injected with high doses of virus in a Phase II clinical trial. More than 20% of injected tumors responded completely [31]. Based on these encouraging data, a Phase III trial was initiated, but this trial was not pursued, largely because of financial and corporate policies (development of ONYX-015 fell to Pfizer, New York, NY, as part of a corporate merger in 1997). Other clinical studies have continued, however. For example, T. Reid and coworkers developed a protocol for treating metastatic colon cancer via hepatic artery infusion [39,40]. This approach results in high doses of virus delivery directly to tumor beds in the liver, which receive most of their blood supply from the hepatic artery. In theory, this circumvents the problem of virus dilution encountered by i.v. infusion, and has two potential benefits: high concentration of virus at the site of delivery is expected to increase efficiency of infection and reduces the impact of neutralizing antibodies that develop during repeated dosing. In this study, about half of treated patients became viremic, producing an estimated 10e11 genomes of virus over a period of days after infusion. Significant clinical responses were observed, but this was in a Phase II setting and was not randomized or compared directly with a control group. Further studies are required to evaluate the effectiveness of this agent more thoroughly. One variable that may affect the outcome of such a trial is the expression of the receptor for adenovirus infection [41]. This protein, referred to as Coxsackie adenovirus receptor (CAR) is expressed primarily in epithelial cells and, like other epithelial cell markers, is downregulated in some tumors [42]. About 50% of metastatic colon cancers downregulate CAR, through the action of the Ras pathway, which is hyperactivated in such cells [43–45]. It is therefore possible that ONYX015 is more effective in patients in whose tumors CAR remains at high levels. Alternatively, CAR could be upregulated by pharmacological intervention; we recently reported that MEK

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inhibitors upregulate CAR expression, resulting in increased infectivity and more than 10-fold increase in virus production. Although many tumors show decreased CAR expression as they become progressively more malignant, we were surprised to discover that metastatic prostate cancer cells have high levels of CAR—far higher than high-grade local tumors [46]. This suggests that metastatic prostate cancer may be a suitable target for adenoviral therapy, at least from the perspective of infectivity. Clearly, this disease will need to be treated by systemic administration of virus, and production of neutralizing antibodies will need to be suppressed. To this end, a clinical study has been initiated to investigate the effect of pretreating patients with Rituxan to prevent expansion of B-cells and suppress production of neutralizing antibodies. If successful, this approach could open a number of possibilities for future use of adenoviruses and other oncolytic agents. CONCLUSION AND FUTURE PROSPECTS We and others have created viruses whose replication depends on loss of the tumor suppressors RB and p53. These viruses kill cancer cells selectively and have shown promising preclinical and clinical evidence of efficacy. Future development of this technology will depend on a clear understanding of factors that limit viral spread in vivo and effective ways of preventing accumulation of neutralizing antibodies that must limit systemic efficacy. These are issues that need to be addressed in the clinical setting, to a large degree, because suitable animal models are not available. The agents that have been developed so far have proven safe and provide a solid foundation for the future development of this relatively new field. New agents that express transgenes to increase potency may be the next wave of this technology. In the meantime, I anticipate that existing agents such as ONYX-015 can be improved tremendously through combination therapy, without compromising the excellent safety profile that has been demonstrated so far. There is therefore good reason to believe that oncolytic viruses will become useful clinical agents that help decrease the morbidity and mortality associated with human cancer.


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ACKNOWLEDGMENTS AND AFFILIATIONS The author is a share holder in ONYX Pharmaceuticals and is supported, in part, by ONYX. I wish to thank my colleagues, Ali Fattaey, Leisa Johnson, Jerry Shen, and Aleida Perez, from ONYX, and Clodagh O’Shea, Allan Balmain, and Michael Korn from University of California–San Francisco for their excellent contributions to this program. REFERENCES 1. Sherr CJ. Cancer cell cycles Science 1996; 274:1672–1677. 2. Sherr CJ, McCormick F. The RB and p53 pathways in cancer Cancer Cell 2002; 2:103–112. 3. Dyson N. The regulation of E2F by pRB-family proteins Genes Dev 1998; 12:2245–2262. 4. Sherr CJ. Tumor surveillance via the ARF-p53 pathway Genes Dev 1998; 12:2984–2991. 5. Mymryk JS, Bayley ST. Multiple pathways for activation of E2A expression in human KB cells by the 243R E1A protein of adenovirus type 5 Virus Res 1994; 33:89–97. 6. Shepherd SE, Howe JA, Mymryk JS, Bayley ST. Induction of the cell cycle in baby rat kidney cells by adenovirus type 5 E1A in the absence of E1B and a possible influence of p53 J Virol 1993; 67:2944–2949. 7. Howe JA, Bayley ST. Effects of Ad5 E1A mutant viruses on the cell cycle in relation to the binding of cellular proteins including the retinoblastoma protein and cyclin A Virology 1992; 186: 15–24. 8. Wang HG, Draetta G, Moran E. E1A induces phosphorylation of the retinoblastoma protein independently of direct physical association between the E1A and retinoblastoma products Mol Cell Biol 1991; 11:4253–4265. 9. Wang HG, Rikitake Y, Carter MC, et al. Identification of specific adenovirus E1A N-terminal residues critical to the binding

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of cellular proteins and to the control of cell growth J Virol 1993; 67:476–488. 10. McCormick F. ONYX-015 selectivity and the p14ARF pathway Oncogene 2000; 19:6670–6672. 11. Barker DD, Berk AJ. Adenovirus proteins from both E1B reading frames are required for transformation of rodent cells by viral infection and DNA transfection [published erratum appears in Virology 1987 May;158(1):263] Virology 1987; 156: 107–121. 12. Yew PR, Berk AJ. Inhibition of p53 transactivation required for transformation by adenovirus early 1B protein Nature 1992; 357:82–85. 13. Yew PR, Liu X, Berk AJ. Adenovirus E1B oncoprotein tethers a transcriptional repression domain to p53 Genes Dev 1994; 8: 190–202. 14. Teodoro JG, Branton PE. Regulation of p53-dependent apoptosis, transcriptional repression, and cell transformation by phosphorylation of the 55-kilodalton E1B protein of human adenovirus type 5 J Virol 1997; 71:3620–3627. 15. Teodoro JG, Branton PE. Regulation of apoptosis by viral gene products J Virol 1997; 71:1739–1746. 16. Teodoro JG, Halliday T, Whalen SG, Takayesu D, Graham FL, Branton PE. Phosphorylation at the carboxy terminus of the 55-kilodalton adenovirus type 5 E1B protein regulates transforming activity J Virol 1994; 68:776–786. 17. Querido E, Marcellus RC, Lai A, et al. Regulation of p53 levels by the E1B 55-kilodalton protein and E4orf6 in adenovirusinfected cells J Virol 1997; 71:3788–3798. 18. Nevels M, Rubenwolf S, Spruss T, Wolf H, Dobner T. The adenovirus E4orf6 protein can promote E1A/E1B-induced focus formation by interfering with p53 tumor suppressor function Proc Natl Acad Sci U S A 1997; 94:1206–1211. 19. Steegenga WT, Riteco N, Jochemsen AG, Fallaux FJ, Bos JL. The large E1B protein together with the E4orf6 protein target p53 for active degradation in adenovirus infected cells Oncogene 1998; 16:349–357.


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20. Whyte P, Buchkovich KJ, Horowitz JM, et al. Association between an oncogene and an anti-oncogene: the adenovirus E1A proteins bind to the retinoblastoma gene product Nature 1988; 334:124–129. 21. Johnson L, Shen A, Boyle L, et al. Selectively replicating adenoviruses targeting deregulated E2F activity are potent, systemic antitumor agents Cancer Cell 2002; 1:325–337. 22. Helin K, Harlow E. Heterodimerization of the transcription factors E2F-1 and DP-1 is required for binding to the adenovirus E4 (ORF6/7) protein J Virol 1994; 68:5027–5035. 23. Neill SD, Nevins JR. Genetic analysis of the adenovirus E4 6/ 7 trans activator: interaction with E2F and induction of a stable DNA-protein complex are critical for activity J Virol 1991; 65: 5364–5373. 24. Raychaudhuri P, Bagchi S, Neill SD, Nevins JR. Activation of the E2F transcription factor in adenovirus-infected cells involves E1A-dependent stimulation of DNA-binding activity and induction of cooperative binding mediated by an E4 gene product J Virol 1990; 64:2702–2710. 25. Neill SD, Hemstrom C, Virtanen A, Nevins JR. An adenovirus E4 gene product trans-activates E2 transcription and stimulates stable E2F binding through a direct association with E2F Proc Natl Acad Sci U S A 1990; 87:2008–2012. 26. Reichel R, Neill SD, Kovesdi I, Simon MC, Raychaudhuri P, Nevins JR. The adenovirus E4 gene, in addition to the E1A gene, is important for trans-activation of E2 transcription and for E2F activation J Virol 1989; 63:3643–3650. 27. O’Connor RJ, Hearing P. Mutually exclusive interaction of the adenovirus E4-6/7 protein and the retinoblastoma gene product with internal domains of E2F-1 and DP-1 J Virol 1994; 68: 6848–6862. 28. Fueyo J, Gomez-Manzano C, Alemany R, et al. A mutant oncolytic adenovirus targeting the Rb pathway produces antiglioma effect in vivo Oncogene 2000; 19:2–12. 29. Heise C, Hermiston T, Johnson L, et al. An adenovirus E1A mutant that demonstrates potent and selective systemic antitumoral efficacy Nat Med 2000; 6:1134–9.

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30. Bischoff JR, Kirn DH, Williams A, et al. An adenovirus mutant that replicates selectively in p53-deficient human tumor cells. Comments Science 1996; 274:373–376. 31. Khuri FR, Nemunaitis J, Ganly I, et al. a controlled trial of intratumoral ONYX-015, a selectively-replicating adenovirus, in combination with cisplatin and 5-fluorouracil in patients with recurrent head and neck cancer Nat Med 2000; 6:879–885. 32. Rothmann T, Hengstermann A, Whitaker NJ, Scheffner M, zur Hausen H. Replication of ONYX-015, a potential anticancer adenovirus, is independent of p53 status in tumor cells J Virol 1998; 72:9470–9478. 33. Heise C, Sampson-Johannes A, Williams A, McCormick F, Von Hoff DD, Kirn DH. ONYX-015, an E1B gene-attenuated adenovirus, causes tumor-specific cytolysis and antitumoral efficacy that can be augmented by standard chemotherapeutic agents. Comments Nat Med 1997; 3:639–645. 34. Turnell AS, Grand RJA, Gallimore PH. The replicative capacities of large E1B-null group A and group C adenoviruses are independent of host cell p53 status. In process citation J Virol 1999; 73:2074–2083. 35. Goodrum FD, Ornelles DA. p53 status does not determine outcome of E1B 55-kilodalton mutant adenovirus lytic infection J Virol 1998; 72:9479–9490. 36. Harada JN, Berk AJ. p53-Independent and -dependent requirements for E1B-55K in adenovirus type 5 replication J Virol 1999; 73:5333–5344. 37. Ries SJ, Brandts CH, Chung AS, et al. Loss of p14ARF in tumor cells facilitates replication of the adenovirus mutant dl1520 (ONYX-015) Nat Med 2000; 6:1128–1133. 38. Shen Y, Kitzes G, Nye JA, Fattaey A, Hermiston T. Analyses of single-amino-acid substitution mutants of adenovirus type 5 E1B-55K protein J Virol 2001; 75:4297–4307. 39. Reid T, Galanis E, Abbruzzese J, et al. Hepatic arterial infusion of a replication-selective oncolytic adenovirus (dl1520): phase II viral, immunologic, and clinical endpoints Cancer Res 2002; 62:6070–6079.


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40. Reid T, Warren R, Kirn D. Intravascular adenoviral agents in cancer patients: lessons from clinical trials Cancer Gene Ther 2002; 9:979–986. 41. Bergelson JM, Cunningham JA, Droguett G, et al. Isolation of a common receptor for Coxsackie B viruses and adenoviruses 2 and 5 Science 1997; 275:1320–1323. 42. Li Y, Pong RC, Bergelson JM, et al. Loss of adenoviral receptor expression in human bladder cancer cells: a potential impact on the efficacy of gene therapy Cancer Res 1999; 59:325–330. 43. Anders M, Christian C, McMahon M, McCormick F, Korn WM. Inhibition of the Raf/MEK/ERK pathway up-regulates expression of the Coxsackie virus and adenovirus receptor in cancer cells Cancer Res 2003; 63:2088–2095. 44. Anders U, Korn O. Model selection in neural networks Neural Netw 1999; 12:309–323. 45. Anders M, Hansen R, Ding RX, Rauen KA, Bissell MJ, Korn WM. Disruption of 3D tissue integrity facilitates adenovirus infection by deregulating the coxsackievirus and adenovirus receptor Proc Natl Acad Sci U S A 2003; 100:1943–1948. 46. Rauen KA, Sudilovsky D, Le JL, et al. Expression of the Coxsackie adenovirus receptor in normal prostate and in primary and metastatic prostate carcinoma: potential relevance to gene therapy Cancer Res 2002; 62:3812–3818.

Epilogue: ‘‘Damn the Torpedoes! Full Speed Ahead!’’* JOSEPH G. SINKOVICS JOSEPH C. HORVATH

The concise summaries of their recent work that the invited authors submitted for this volume, reflect well the state of virus therapy for human cancers. After a protracted and difficult beginning many decades ago, now major advances are being made both in the selection of naturally oncolytic viruses, but above all, in the creation of genetically engineered viruses

*

After Admiral David Glasgow Farragut (1801–1870) exclaiming over the mine fields of Mobile Bay, AL, on August 5, 1864 (and getting through!). 797

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that attack tumors highly selectively. Either the promoters that drive these viruses are restricted to certain malignantly transformed tissues, or the viral genome is altered in such a way that normal cells would eliminate the virus, the task that tumor cells due to their own genetic defects can not accomplish. Another generation of genetically engineered viruses insert genes into the genome of tumor cells. These are tumorsuppressor genes, cytokine genes, genes of immunological costimulators, and genes that trigger cell suicide. A set of viral vectors deliver antisense oligonucleotides (As-ODN) that antagonize the replication of genomic sequences of oncogenes and fusion oncoproteins, or those of genes that promote neoangiogenesis. The tumor cell can now be attacked at many levels of its operation. What are the most prominent intracellular targets at which virotherapy should be aimed, and can multiple targets be attacked at the same time simultaneously or sequentially? Naturally oncolytic viruses encounter little, if any opposition, to their full replicative cycles in tumor cells with downregulated interferon production machinery. Certain oncoproteins, especially those encoded by the c-ras family of oncogenes, inactivate the protein kinase (PKR) system, which is essential for the initiation of interferon production within the normal but virally infected cell. If farnesyltransferase inhibitors of the c-ras→Ras pathway restore cell metabolism, shifting it toward normalization, these tumor cells may regain PKR activity, produce interferon, and eliminate a ‘‘naturally oncolytic’’ virus, thereby escaping tumor cell lysis. This would be a system in which a biologically active molecular mediator and a naturally oncolytic virus could not cooperate. However, genetically engineered viruses depositing the herpesviral tk gene in these tumor cells still could be tested in combination with farnesyltransferase inhibitors. R115777 reduces hypoxia, induces oxygenation, and reduces neovascularization of human glioblastoma xenografts [1]. It should be tested in combination with a genetically engineered oncolytic virus for which excellent candidates are the polio-rhinoviral recombinants developed at Duke University, Durham, NC.

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Other designated targets for oncolytic virotherapy are the insulinlike growth factor receptor-I and ligand (IGF-I and R) systems; the survivins; the proteasomes; the telomeres; the notorious epidermal growth factor (EGF)-R; and the neoangiogenesis inducer gene product proteins, from vascular endothol growth factor (VEGF) to the hepatocyte growth factor/scatter factor (HGF/SF), reacting with its receptor c-Met [2]. Insulin-like growth factor and its receptor form para- and autocrine circuits to promote tumor cell growth, whereas IGFbinding protein-related protein-1 (IGFBP-rP1) antagonizes the system and induces apoptosis in those tumor cells that may overexpress it [3]; however, its gene is silenced by hypermethylation in tumor cells. After demethylating it with 5-azadC, the suppressed gene of IGFBP-rP1 in prostate cancer cells or in stromal cells of the tumor bed regains its function. Prostate cancer cells transfected with the IGFBP-rP1 gene lost a great deal of their malignant behavior: Their growth rate was reduced, they formed no colonies in soft agar, and they succumbed to apoptosis [3]. This is one of the candidate genes for reinsertion into the genome of tumor cells by adeno- or adenoassociated viruses. Insulin-like growth factor-IR emits antiapoptotic signals through the Ras pathway, such as the activation of PI3K/Akt and the translocation of Raf-1 protein into mitochondria. However, soluble sIGF-IR, acting as a decoy, blocks the activity of the real receptor and thereby inhibits the growth of ovarian carcinoma cells [4]. Overexpression of the growth-inhibitory insulin receptor-related receptor and the nerve growth factor receptor (NGF-R/TrkA) by neuroblastoma cells overrules the tumor-promoting effects of the amplified N-Myc and that of the ligand-activated IGF-IR [5]. These are the inhibitory genes that need to be reinserted into neuroblastoma cells by viral vectors. There is a fully human monoclonal antibody specific to IGF-IR [6]. Its administration should be combined with the adenoviral vectors that encode decoy receptors antigenically different from the real receptor or the proteins that are antagonistic to IGF-IR. Survivin emerges as one of the most powerful anti-apoptotic proteins operational in neoplastic cells. The survivin protein is recognized by T lymphocyte clones of the tumor-bearing

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host. These T cell clones may be expanded and may exert cytotoxicity on survivin-expressing tumor cells in a HLA-A2–restricted fashion [7,8]. Autologous CD34Ⳮ stem cells in the bone marrow are spared by these clones of immune T cells. Antisurvivin plasmids containing a reverse primer (pcDNA3-survivin) inhibited tumorigenicity of gastric carcinoma cells [9]; so does the Thr34Ala survivin mutant gene-carrier adenovirus. In a sequential fashion, immune T cell therapy followed by adenoviral therapy to eliminate the remaining survivinexpressing tumor cells that survived the lymphocyte attack appears to be feasible. The short-living survivin protein is usually destroyed in proteasomes [10], an event that would favor the tumor-bearing host. Retroviral vector pMSCV-Fas achieves the same effect [11]. Destruction of survivin in proteasomes is promoted by interferon (IFN)-␥. Interferon-␥–treated colon carcinoma cells also overexpress the CD95 Fas receptor, rendering these tumor cells more apoptosis-prone when binding FasL [11]. However, the multicatalytic proteasome system often destroys pro-apoptotic proteins (p53; Bax) within the tumor cell. Proteasome inhibitors such as bortezomib or lactacystin can preserve the intracellular pro-apoptotic proteins in tumor (multiple myeloma and many other) cells. Would the Mayo Clinic’s measles virus act additively or even synergistically with bortezomib in the treatment of multiple myeloma? If another viral vector delivery of proteasome inhibitors at a critical phase of the cell cycle could antagonize MDM and thereby rescue p53 protein from destruction, the tumor cell would remain susceptible to programmed death. Regarding sarcomas, activin receptor-like kinases, especially Alk1 and Alk5, act as signal receptors for transforming growth factor (TGF)-␤, a growth factor for many of these tumors. The Alk4/5/7 inhibitor SB-431542, in combination with imatinib, suppressed proliferation of osteosarcoma cells. Imatinib acted against TGF-␤–induced platelet-derived growth factor (PDGF) production in these cells, which is another growth factor for many sarcoma cells [12]. Imatinib suppresses the PDGF circuits in gastrointestinal stromal tumor (GIST) and in pancreatic carcinoma cells [13,14]. The same circuit

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could be targeted by As-ODN carrier adenoviruses. Rhabdomyosarcoma cells are driven by HGF/SF, the ligand of the receptor c-Met. In addition, these tumor cells also express the CXC chemokine receptor-4 and respond to its ligand, SDF-1 [15]. Histone deacetylase inhibitors (suberoylanilide hydroxamide acid or SAHA; pyroxamide) induce apoptotic death of rhabdomyosarcoma cells [16]. Cytomegalovirus and herpesvirus G207 kill rhabdomyosarcoma cells (Cincinnati Children’s Hospital, Cincinnati, OH, and MediGene, San Diego, CA). G207 and SAHA should be administered in combination first in xenografts and then in a clinical trial. Ewing sarcoma cells express the chimeric EWS/ETS oncoprotein resulting from chromosome breaks and translocations forming t(11;22)(q24;q12) [17]. The fused oncoprotein activates the telomerase system. These tumor cells also overexpress the adhesion molecule MUC18, which was discovered in melanoma cells but is overexpressed in many other tumors, including osteosarcomas [18]. A fully human monoclonal antibody, ABX-MA1, suppresses the metastatic spread of xenografts of these tumors [18]. The E1A adenoviral type 5 gene inserted into tumor cells by many different means inhibits tumor growth and induces apoptosis in tumor cells. In Ewing’s sarcoma cells, AdE1A downregulated HER2/ neu expression and suppressed VEGF production [19]. Trastuzumab (Herceptin, Genentech, South San Francisco, CA) and AdE1A administered in combination is a therapeutic modality for this tumor and is to be tested soon in clinical trials. Mesothelioma cells overexpress cyclooxygenase-2 and this pathway is blocked by rofecoxib. Cyclooxygenase-2 inhibition combined with the administration of Ad.IFN␤ induced tumor-attacking CD8Ⳮ T cell clones [20]. Roscovitine, the inhibitor of cycline-dependent kinases, induces apoptotic death in HTLV-1–transformed leukemic T cells [21]. The H. L. Moffitt Cancer Center, Tampa, FL, will use it against sarcoma cell lines either alone or in combination with other agents in preparation for a clinical trial. Antibodies aimed at the PDGF-R and Ad.E1A are good candidates for possible additive action with cycline-dependent kinase inhibitors. It has been discovered that the ansamycin 17-N-allylamino-17-demethyl geldanamycin synergizes with radio-

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and chemotherapy for prostatic carcinoma [22]. Geldanamycins inhibit heat shock protein 90; and ZD1839 (gefitinib) suppresses signal transduction (Akt activation) from ErbB2 in breast cancer cells, thereby removing a major blockade of apoptotic death [23]. Because suppressors of oncogene signal pathways work best in combinations, naturally oncolytic and genetically engineered viruses should be applied in the same manner. For a combination to be tested, a good candidate is GGTI-2154, a geranylgeranyl transferase inhibitor that readily induces apoptotic death of H-Ras–dependent murine breast cancers [24]. A mouse mammary virus-related retroviral agent exists in some human breast cancers; this association may render these tumor cells more susceptible to an external viral attack, inasmuch as viruses frequently interfere with one another. Geldanamycins and certain inhibitors of oncogenic kinase autophosphorylation and viral vectors antagonizing the oncogene itself appear to be reasonable candidates for combined protocols. Further services that genetically engineered adenoviruses could render to the tumor-bearing host are transduction of the interleukin (IL)-12 gene into macrophages of the tumor bed (AdmIL-12) [25] for instigating an antitumor attack by the transduced macrophages. Further, an adenoviral construct (Ad5-TERT-E1) replicating exclusively under the control of human telomerase reverse transcriptase selectively lyses prostate cancer cells [26]. A replication-defective adenovirus (Introgen, Houston, TX) replaces the wild-type p53 in tumor cells. ONYX-015 targeting p53-deficient tumor cells now performs well in the oral cavity as a mouthwash in resolving premalignant dysplastic lesions, predecessors of squamous cell carcinomas [27,28], proving that simplistic technology of administration of an oncolytic virus may not be second in therapeutic value to a sophisticated mode of administration. The question immediately arises: Could the new live attenuated influenza A viral vaccine (Flumist, Wyeth/MedImmune, Gaithersburg, MD; Physicians Desk Reference, 2004; pp 3424–3427) have any role in the treatment of squamous cell carcinomas of the oronasal cavities?

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The long list of agents targeting the most notorious EGF-R (ZD1839, gefitinib; OSI-774, erlotinib; CI-1033; C225, cetuximab; ABX-EGF; EGF-P64K vaccine; DAB389 EGF immunotoxin) contains no viral agent [29]. Is there a major obstacle that would doom to failure any attack on EGF-R by naturally oncolytic or genetically engineered viruses? We could recognize none. Cytomegalovirus (CMV) enters cells through the EGF-R [30]. If tumor cells over expressing EGF-R were increasingly accessible to CMV entry, would apathogenic oncolytic variants of CMV selectively attack these cells? Amphiregulin (AR) activates EGF-R which, in turn, induces overexpression of the malignant phenotype-associated cell-surface protein, the extracellular matrix metalloprotease receptor-inducer. Antisense cDNA aimed at the interaction of AR and EGF-R reduces tumorigenicity of breast cancer cells [31]. Adenoviral vectors could deliver the AR antisense sequences and break the circuit. In addition to delivering suicide and cytokine genes into tumor cells, some viruses deliver genes of enzymes that render prodrugs to be effective chemotherapeutic agents within the affected cells. Of the long list of these viral vectors, the latest is vesicular stomatitis virus (VSV), delivering the gene of cytosine deaminase/uracil phosphoribosyl transferase into tumor (mouse breast cancer) cells, rendering the tumor cells highly susceptible to 5-FU and inducing extensive bystander effect [32]. Viruses may render chemotherapy-resistant human tumor cells sensitive to selected chemotherapeutical agents. The latest results with high dose IV virotherapy of various human tumors using a newly applied strain of NDV and resulting in partial remissions and stabilizations of disease have recently been reviewed [33]. Most recent reports now in print suggest that some (not all) chemoradiotherapy-resistant glioblastoma multiforme tumor cells remain susceptible to oncolysis by NDV [34,35]. It is most remarkable that different NDV strains (73T, Ulster, PV701, LaSota, OV001, and the veterinary attenuated vaccine strain renamed MTH-68H) all exert oncostatic-oncolytic effects either by apoptosis induction and/or by mobilizing host immune reactions against NDVinfected tumor cells, and that antiviral immune globulin pro-

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duction does not inhibit oncolysis, and that no immune complex disease ensues (it has not been reported) after repeated administration through different routes of small to very large doses of the virus. The Proceedings of the American Society of Clinical Oncology (ASCO) 40th Annual Meeting held in New Orleans, Louisiana, in June 2004 contains an abstracted description of successful treatment for cutaneous lymphomas with an adenoviral vector of the IFN-␥ cDNA. The Proceedings of the American Association for Cancer Research (AACR) 95th Annual Meeting held in Orlando, Florida, in March 2004 contains several abstracted reports on oncolysis of human cancer cells by fusogenic and other oncolytic herpes viruses (Synco2D; NV1023; NV1066; OncoVEX GM-CSF; G207; MGH1), a triple-mutated vaccinia virus (vSPT), and genetically engineered adenoviruses (CG5757, CG8840, adenoviruses driven by VEGF or survivin specifically attacking malignant glioma cells, and the hTERT promoter-driven and endostatin gene containing CNHK300-mE adenoviral construct). As to immune T cells, not only the amplified antiapoptotic survivins but also the amplified or mutated telomere systems engender the rise of such autologous clones [36–38]. Some mixed clones of NK and T cells may be implicated to induce tumor cell (chondrosarcoma) differentiation, senescence, and death [39]. When rituximab-coated human lymphoma cells are phagocytized and digested by autologous dendritic cells (DC), lymphoma-associated antigens expressed by these DC induce tumor rejection-strength immune reactions mediated by T cell clones [40]. Patients with advanced arteriosclerosis/atheromatosis circulate CD4 T cells that kill smooth muscle cells in the arterial cell walls; these lymphocyte clones are cytotoxic to allogenic leiomyosarcoma cells [41]. Expanded clones of immune T cells and/or NK cells (LAK cells) are not to be discounted, they remain strong agents of adoptive immunotherapy. The human multiple-drug-resistance-1 gene is transcriptionally activated by the YB-1 protein, when this protein translocalizes into the nucleus. Further, YB-1 interacts with p53 and suppresses the fas gene, thus exerting anti-apoptotic effects. Intranuclear overexpression of YB-1 protein occurs in

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breast, colon, lung, gastric, ovarian, and pancreatic carcinomas and in osteosarcoma cells, and YB-1 mRNA is overexpressed in glioblastoma and melanoma cells. E1A-mutated (Ad520; dl520) or E1A-deleted (Ad312) adenoviruses are replication-defective in normal cells, but replicate to full viral particle maturation and cytolysis in malignantly transformed MDR cells, in which nuclear YB-1 is overexpressed. Cell stress by irradiation, chemotherapy, or hyperthermia promotes YB-1 translocation into the nucleus and thereby facilitates full oncolytic replication of Ad520 in such cells. Whereas P-glycoprotein–overexpressing MDR tumor cells resist enveloped (myxoand paramyxo-) oncolytic viruses [42], these very same tumor cells are susceptible to, and succumb to, full replicative cycles of Ad520 [43]. Tumor growth and its acceleration or inhibition remains a most treacherous territory, when it comes to scientifically designed interventions. No single biological agent emerges as being able to render full and lasting reversal of the oncogenic pathways that are operational in malignantly transformed cells. However, we begin to recognize two- or three-agent combinations that appear to approach this effect, whether applied synchronously or sequentially. It is not the xenograft assays, but the clinical trials that identify the most effective combinations. When biological agents are powerful constituents of these combined treatment regimens, lower and less toxic doses of chemotherapeuticals can exert their full efficacy. In some fully biologically combined regimens, the effects match those of the highest dosages of chemotherapy, especially in notoriously chemotherapy-resistant tumors (glioblastoma, melanoma, kidney carcinoma). One member of biologically combined regimens should be an oncolytic virus. Even when the virus is replication-deficient and works by apoptosis induction, apoptosomes of tumor cells within incompletely lysed tumor masses could immunize the host through dendritic cell (DC)→T cell interaction or by evoking ADCC reactions involving natural killer (NK) cells or macrophages for further antitumor effects. Some sort of a special co-expression of tumor and viral antigens occurs in viral oncolysates (VO). It should be studied further, whether VO are more efficient means of tumor lysis in-

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duction and active tumor-specific immunization than the postoncolytic immunity elicited by a naturally oncolytic virus; and if viruses other than influenza A or Newcastle disease virus (NDV) (such as reovirus or VSV) could produce oncolysates efficient in tumor lysis and antitumor immunization. Indeed, viral oncolysates contain tumor cell apoptosomes, solubilized tumor-associated antigens, and viral antigens budding from tumor cell membranes. Viral oncolysates are expected to co-stimulate DC→T cell interactions as well as mobilize NK/ NKT cell populations. Viral oncolysates may act efficiently against micrometastases, but seldom score as therapeutic vaccines working against established metastatic tumors. Some DC vaccines may exert this high level of efficacy. When a DC vaccine consists of an inactivated tumor cell fused with a live mature, autologous DC, the fusogenic protein may be the contribution of a viral agent (herpesvirus; NDV; VSV). Virotherapy could re-orient the stroma of the tumor bed, rendering it from a supportive network in collusion with the tumor to an indifferent bystander or, better, an army of warriors launching an attack on the tumor at many levels—denying blood supply to it or actually expressing hostility to it with the production of molecular mediators, inducers of apoptosis in the tumor cells. Thus, virotherapy should find its integrated place within the combination regimens that forecast the new biological therapy of cancer. REFERENCES 1. Delmas C, End D, Rochaix P, Favre G, Toulas C, Cohen-Jonathan E. The farnesyltransferase inhibitor R115777 reduces hypoxia and matrix metalloproteinase 2 expression in human glioma xenografts Clin Cancer Res 2003; 9:6062–6068. 2. Sengupta S, Sellers LA, Cindrova T, Skepper J, Gherardi E, Sasisekharan R, Fan T-PD. Cyclooxygenase-2-selective nonsteroidal anti-inflammatory drugs inhibit hepatocyte growth factor/scatter factor-induced angiogenesis Cancer Res 2003; 63: 8351–8359. 3. Mutaguchi K, Yasumoto H, Mita K, Matsubara A, Shiina H, Igawa M, Dahiya R, Usui T. Restoration of insulin-like growth

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factor binding protein-related protein 1 has a tumor suppressive activity through induction of apoptosis in human prostate cancer Cancer Res 2003; 53:7717–7723. 4. Hongo A, Kuramoto H, Nakamura Y, Hasegawa K, Nakamura K, Kodama J, Hiramatsu Y. Antitumor effects of a soluble insulin-like growth factor I receptor in human ovarian cancer cells: advantage of recombinant protein administration in vivo Cancer Res 2003; 63:7834–7839. 5. Weber A, Huesken C, Bergmann E, Kiess W, Christiansen NM, Christiansen H. Coexpression of insulin receptor-related receptor and insulin-like growth factor 1 receptor correlates with enhanced apoptosis and dedifferentiation in human neuroblastomas Clin Cancer Res 2003; 9:5683–5692. 6. Burtrum D, Zhu Z, Lu D, Anderson DM, Prewett M, Pereira DS, Bassi R, Abdullah R, Hooper AT, Koo H, Jimenez X, Johnson D, Apblett R, Kussie P, Bohlen P, Witte L, Hicklin DJ, Ludwig DL. A fully human monoclonal antibody to the insulin-like growth factor I receptor blocks ligand-dependent signaling and inhibits human tumor growth in vivo Cancer Res 2003; 63:8912–8921. 7. Reed JC, Wilson DB. Cancer immunotherapy targeting survivin Clin Cancer Res 2003; 9:6310–6315. 8. Pisarev V, Yu B, Salup R, Sherman S, Altieri DC, Gabrilovich DI. Full-length dominant-negative survivin for cancer immunotherapy Clin Cancer Res 2003; 9:6523–6533. 9. Tu SP, Jiang XH, Lin MC, Cui JT, Yang Y, Lum CT, Zou B, Zhu YB, Jiang SH, Wong WM, Chan AO-O, Yuen MF, Lam SK, Kung HF, Wong C-Y. Suppression of survivin expression inhibits in vivo tumorigenicity and angiogenesis in gastric cancer Cancer Res 2003; 63:7724–7732. 10. Voorhees PM, Dees EC, O’Neil B, Orlowski RZ. The proteasome as a target for cancer therapy Clin Cancer Res 2003; 9: 6316–6325. 11. Geller J, Petak I, Szekely Szucs K, Nagy K, Tillman DM, Houghton JA. Interferon-␥-induced sensitization of colon carcinomas to ZD9331 targets caspases, downstream of Fas, independent of mitochondrial signaling and the inhibitor of apoptosis survivin Clin Cancer Res 2003; 9:6504–6515.

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12. Matsuyama S, Iwadate M, Kondo M, Saitoh M, Hanyu A, Shimizu K, Aburatani H, Mishima HK, Imamura T, Miyazono K, Muiyazawa K. DSB-431542 and Gleevec inhibit transforming growth factor-␤-induced proliferation of human osteosarcoma cells Cancer Res 2003; 63:7791–7798. 13. Heinrich MC, Corless CL, Demetri GD, Blanke CD, von Mehren M, Joensuu H, McGreevey LS, Chen C-J, Van den Abbeele AD, Druker BJ, Kiese B, Eisenberg B, Roberts PJ, Singer S, Fletcher CDM, Silberman S, Dimitrijevic S, Fletcher JA. Kinase mutations and imatinib response in patients with metastatic gastrointestinal stromal tumor J Clin Oncol 2003; 21: 4342–4349. 14. Hwang RF, Yokoi K, Bucana CD, Tsan R, Killion JJ, Evans DB, Fidler IJ. Inhibition of platelet-derived growth factor receptor phosphorylation by STI571 (Gleevec) reduces growth and metastasis of human pancreatic carcinoma in an orthotopic nude mouse model Clin Cancer Res 2003; 9:6534–6544. 15. Jankowski K, Kucia M, Wysoczynski M, Reca R, Zhan D, Tryzna E, Trent J, Peiper S, Zembala M, Ratajczak J, Houghton P, Janowska-Wieczorek A, Ratajczak MZ. Both hepatocyte growth factor (HGF) and stromal-derived factor-1 regulate the metastatic behavior of human rhabdomyosarcoma cells, but only HGF enhances their resistance to radiotherapy Cancer Res 2003; 53:7926–7935. 16. Kutko MC, Glick RD, Butler LM, Coffey DC, Rifkind RA, Marks PA, Richon VM, LaQuaglia MP. Histone deacetylase inhibitors induce growth suppression and cell death in human rhabdomyosarcoma in vitro Clin Cancer res 2003; 9:5749–5755. 17. Takahashi A, Higashino F, Aoyagi M, Yoshida K, Itoh M, Kyo S, Ohno T, Taira T, Ariga H, Nakajima K, Hatta M, Kobayashi M, Sano H, Kohgo T, Shindoh M. EWS/ETS fusions activate telomerase in Ewing’s tumors Cancer Res 2003; 63:8338–8344. 18. McGary EC, Heimberger A, Mills L, Weber K, Thomas GW, Shtivelband M, Chelouche Lev D, Bar-Eli M. A fully human antimelanoma cellular adhesion molecule/MUC18 antibody inhibits spontaneous pulmonary metastasis of osteosarcoma cells in vivo Clin Cancer Res 2003; 9:6560–6566.

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19. Zhou Z, Zhou R-R, Guan H, Bucana CD, Kleinerman ES. E1A gene therapy inhibits angiogenesis in a Ewing’s sarcoma animal model Mol Cancer Ther 2003; 21:1313–1319.. 20. DeLond P, Tanaka T, Kruklitis R, Henry AC, Kapoor V, Kaisre LR, Sterman DH, Albelda SM. Use of cyclooxygenase-2 inhibition to enhance the effect of immunotherapy Cancer Res 2003; 63:7845–7852. 21. Mohapatra S, Chu B, Wei S, Djeu J, Epling-Burnette PK, Loughran T, Jove R, Pledger WJ. Roscovitine inhibits STAT5 activity and induces apoptosis in the human leukemia virus type 1-transformed cell line MT-2 Cancer Res 2003; 63:8523–8530. ˚ M, Solit DB, Hiller G, Rosen 22. Enmon R, Yang W-H, Ballangrud A N, Scher HI, Sgouros G. Combination treatment with 17-Nallylamino-17-demethoxy geldanamycin and acute irradiation produces supra-additive growth suppression in human prostate carcinoma spheroids Cancer Res 2003; 63:8393–8399. 23. Xu W, Yuan X, Jung YJ, Yang Y, Basso A, Rosen N, Chung EJ, Treprl J, Neckers L. The heat shock protein 90 inhibitor geldanamycin and the ErbB inhibitor ZD1839 promote rapid PP1 phophatase-dependent inactivation of AKT in Erb2 overexpressing breast cancer cells Cancer Res 2003; 63:7777–7784. 24. Sun J, Okhanda J, Coippola D, Yin H, Kothare M, Busciglio B, Hamilton AD, Sebti SM. Geranylgeranyltransferase I inhibitor GGTI-2154 induces breast carcinoma apoptosis and tumor regression in H-Ras transgenic mice Cancer Res 2003; 63: 8922–8929. 25. Satoh T, Saika T, Ebara S, Kusaka N, Timme TL, Yang G, Wang J, Mouraviev V, Cao G, Abdel Fattah EM, Thompson TC. Macrophages transduced with an adenoviral vector expressing interleukin 12 suppress tumor growth and metastasis in a preclinical metastatic prostate cancer model Cancer Res 2003; 63: 7853–7860. 26. Lanson NA, Friedlander PL, Schwarzenberger P, Kolls JK, Wang G. Replication of an adenoviral vector controlled by the human telomerase reverse transcriptase promoter causes tumor-selective tumor lysis Cancer Res 2003; 63:7936–7941. 27. Ganly I, Singh B. Topical ONYX-015 in the treatment of premalignant oral dysplasia: another role for the cold virus? J Clin Oncol 2003; 21:4476–4478.

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28. Rudin CM, Cohen EEW, Papadimitrakopoulou VA, Silverman S Jr, Recant W, El-Nagger AK, Stenson K, Lippman SM, Hong WK, Vokes EE. An attenuated adenovirus, ONYX-015, as mouthwash therapy for premalignant oral dysplasia J Clin Oncol 2003; 21:4546–4552. 29. Herbst RS, Bunn PA. Targeting the epidermal growth factor receptor in non-small cell lung cancer Clin Cancer Res 2003; 9: 5813–5824. 30. Wang X, Huang SM, Chin ML, Raab-Traub N, Huang ES. Epidermal growth factor receptor is a cellular receptor for human cytomegalovirus Nature 2003; 424:456–461. 31. Menashi S, Serova M, Ma L, Vignot S, Mourah S, Calvo F. Regulation of extracellular matrix metalloproteinase inducer and matrix metalloproteinase expression by amphiregulin in transformed human breast epithelial cells Cancer Res 2003; 63: 7575–7580. 32. Porosnicu M, Mian A, Barber GN. The oncolytic effect of recombinant vesicular stomatitis virus is enhanced by expression of the fusion cytosine deaminase/uracil phosphoribosyltransferase suicide gene Cancer Res 2003; 63:8366–8376. 33. Lorence RM, Pecora AL, Major PP, Hotte SJ, Laurie SA, Roberts MS, Groene WS, Bamat MK. Overview of phase I studies of intravenous administration of PV701, an oncologic virus. Curr Opin Molec Therap 2003; 5:618–624. 34. Csatary LK, Gosztonyi G, Szeberenyi J, Fabian Z, Liszka V, Bodey B, Csatary CM. MTH-68/H oncolytic viral treatment in human high-grade gliomas. J Neurooncol 2004; 67:83–93. 35. Freeman AI, Gomori JM, Linetsky E, Zakay-Rones Z, Panet A, Libson E, Irving CS, Galun E, Siegal T. Phase I/II trial intravenous OV001 oncolytic virus in resistant glioblastoma multiforme. Am Soc Clin Oncol 40th Annual Meeting, New Orleans, June 5–8. Proceedings 2004; 23:110 噛1515. 36. Minev B, Hipp J, Firat H, Schmidt JD, Langlade-Demoyen P, Zanetti M. Cytotoxic T cell immunity against telomerase reverse transcriptase in humans. Proc Nat Acad Sci USA 2000; 97:4796–4801. 37. Hernańdez J, Garcia-Pons F, Lone YC, Firat H, Schmidt JD, Langlade-Demoyen P, Zanetti M. Identification of a human te-

Epilogue

811

lomerase reverse transcriptase of low affinity for HLA A2.1 that induces cytotoxic T lymphocytes and mediates lysis of tumor cells. Proc Nat Acad Sci USA 2002; 99:12275–12280. 38. Vonderheide RH, Schultze JL, Anderson KS, Maecker B, Butler MO, Xia Z, Kuroda MJ, von Bergwelt-Baildon MS, Bedor MM, Hoar KM, Schnipper DR, Brooks MW, Letvin NL, Stephans KF, Wucherpfenning KW, Hanh WC, Nadler LM. Equivalent induction of telomerase-specific cytotoxic T lymphocytes from tumor-bearing patients and healthy individuals. Cancer Res 2001; 61:8366–8370. 39. Sinkovics JG. Chondrosarcoma cell differentiation. Experimental data and possible molecular mechanisms. Pathology Oncology Research 2004 (in print). 40. Franki SN, Levy R, Timmerman JM. Vaccination with dendritic cells co-cultivated with antibody-coated tumor cells provides protective immunity against B cell lymphoma in vivo. 12th Immunology, Montreal, Canada. Clin Investig Medicine 2004; 27:212D Th53.319. 41. Sato K, Kopecky SI, Frye RI, Goronzy JJ, Weyand CM, T cells kill vascular smooth muscle cells via the death pathway. A role for TRAIL-producing T cells in the rupture of the atherosclerotic plaque. 12th Immunology, Montreal, Canada. Clin Investig Medicine 2004; 27:159A M37.45. 42. Raviv Y, Puri A, Blumenthal R. P-glycoprotein-overexpressing multidrug-resistant cells are resistant to infection by enveloped viruses that enter via the plasma membrane FASEB 2000; 14: 511–515. 43. Holm PS, Lage H, Bergmann S, Ju¨rchott K, Glockzin G, Bernshausen A, Mantwill K, Landhoff A, Wichert A, Mymryk JS, Ritter T, Dietel M, Ga¨nsbacher B, Royer H-D. Multidrug-resistant cancer cells facilitate E1-independent adenoviral replication: impact for cancer gene therapy Cancer Res 2004; 64: 322–328.

Index

Acquired immunodeficiency syndrome (AIDS), 6, 263 (see also Human immunodeficiency virus) Activators, promoters, and replacements (APR), 240 Adenoassociated virus (AAV), 68, 70, 71, 72, 159, 160, 628, 629, 648–649 Adenoviral oncolysis, 162–168 Adenoviral vectors, 166 Adenoviruses, 55–68, 163, 167, 801, 802 Animal tumor models, development of, 483–490, 495–510, 520, 646–647 (see also Animal tumor vaccine; Gibbon ape leukemia; Kilham rat viruses; Minute virus of mice) characteristics of memory T cells, 489–490

[Animal tumor models] dormancy studies, 488 Esb model, 483–484 introducing danger models, 484–487 Newcastle disease model, 484 parvoviruses, 646–647 residual tumor cells and immune memory, 489 Animal tumor vaccine (ATV), 495–510, 523 (see also Animal tumor models; Gibbon ape leukemia; Kilham rat viruses; Minute virus of mice) Ansamycin antibiotics, 344–345, 801–802 Anti-neoangiogenesis, 274–290 antisense technology, 287–289 813

814

[Anti-neoangiogenesis] inhibitors of neoangiogenesis, 278–286 monoclonal antibodies, 286–287 vaccines, 289–290 vasculogenesis and angiogenesis, 274–278 Antisense oligonucleotides, 263–274, 336, 798 anti- to pro-apoptosis, 264–272 c-myc, 272–274 viral blockade, 263–264 Antisense technology, 287–289 Antitumor activity, mechanisms of parvoviruses, 642–652, 655 (see also Parvoviruses) animal models, 646–647 evidence of oncolytic effects, 642–645 immune system and tumor clearance, 649–652 tumor cell targets, 647–459 Antitumor immune memory, and control of residual tumor cells, 481–531, 614–615 animal tumor models, development of, 483–490 characteristics of memory T cells, 489–490 dormancy studies, 488 Esb model, 483–484 introducing danger models, 484–487 Newcastle disease model, 484 residual tumor cells and immune memory, 489

Index

[Antitumor immune memory, and control of residual tumor cells] clinical immunotherapy studies, 495–504 autologous virus modified tumor vaccine, 495–497 effects of repeated vaccinations, 500–501 hypersensitivity responses and prognosis, 503–504 nonresponder patients, 503 phase I, optimization of vaccine composition, 497–498 potentiation of antitumor memory response, 502 specificity of responses, 498–500 turning immunological nonresponders into responders, 501–502 conclusions, 516–523 immune memory, 519–523 critical evaluation of standard therapies, 511–516 detrimental effects of chemotherapy, 511–513 economic evaluations, 515–516 rational re-evaluation of standard therapies, 513–515 increasing induced antitumor immunity, 614–615 mouse to man, 490–494 antitumor memory T cells in cancer patients, 491

Index

[Antitumor immune memory, and control of residual tumor cells] conditioning the immune system, 494 Newcastle disease virus infection breaking tolerance, 494 NOD/SCID mice with autologous memory T cells, 491–492 tolerance to tumorassociated antigens, 492–493 introduction, 482–483 side effects, 504–511 conclusions of survival data, 509–511 five-year survival, 505–508 long-term survival, 508–509 overall median survival, 508 phase II clinical vaccination studies, 504–505 two-year survival, 505 summary, 481–482 Apoptosis flavopiridols-induced, 223–224 from anti- to pro-, 264–272 Attenuation of neuropathogenic properties, of poliovirus, 764–766 Autocrine circuits, 340–342 Autologous virus modified tumor vaccine, 495–497 Bacillus Calmette Gue´rin (BCG), 14–15, 17, 18, 29, 40, 80, 693

815

Bacillus anthracis, 4 Bacterial infections, 1 Bacteriophages, 3–4 Biological therapeutics, 149–457 (see also Biotherapy; Chemotherapy; Clinical immunotherapy studies; Viral therapy) anti-neoangiogenesis, 274–290 antisense technology, 287–289 inhibitors of neoangiogenesis, 278–286 monoclonal antibodies, 286–287 vaccines, 289–290 vasculogenesis and angiogenesis, 274–278 antisense oligonucleotides, 263–274 anti- to pro-apoptosis, 264–272 c-myc, 272–274 viral blockade, 263–264 chemokine and cytokine growth factors, 333–343 autocrine circuits, 340–342 catenins, caveolins, and connexins, 339–340 expropriated cytokines, 333–336 matrix metalloproteinases and chemokines, 336–338 mesothelioma, 338–339 virus-induced cytokines and chemokines, 342–343

816

[Biological therapeutics] cyclooxygenase inhibitors, 231–235 eicosanoids, 231–233 nonsteriodal antiinflammatory agents, 233–235 discussion, 451–455 farnesyl transferase inhibitors, 151–172 adenoviral oncolysis, 162–168 c-ras, 151–156 virus attack/host counterattack, 156–162 flavopiridols, 221–226 cyclins, 221–223 flavopiridols-induced apoptosis, 223–224 inhibitors, 224–226 glioblastoma multiformes, 410–425 biotherapy, 418–425 pathogenesis, 410–418 hormone-related events in breast and prostate cancers, 343–350 complex interactions, 343–346 observations, 346–350 introduction, 149–151 metalloproteinase inhibitors, 228–231 inhibitors, 230–231 pathophysiology, 228–230 microvascular tumor bed, 331–333 microvasculature, 331–332 suppressors, 332–333 molecular oncology, recent developments, 235–241 multiple myeloma, 396–410

Index

[Biological therapeutics] biotherapy, 403–410 pathogenesis, 396–403 protein kinase C inhibitors, 226–228 summary, 456–457 telomeres, 321–324 rapamycins, As-ODN, and lymphocytes, 322–324 telomerase, 321–322 tissue cultures, 320–321 trypsin, 321 tyrosine kinase inhibitors, 172–180 imatinib mesylate, 172–177 OSI-774 erlotinib, 179–180 ZD1839 gefitnib, 177–179 viral oncolysis, recent developments, 180–182 xenografts, 324–331, 350–357 activated stroma, 328–329 insulinlike growth factor-R, 327–328 intercellular adhesions, 329–330 miscellaneous agents tested, 350–357 natural hybridomas, 330–331 natural killer cells, 327 paracrine circuits, 324–427 Biotherapy (see also Biological therapeutics; Chemotherapy; Clinical immunotherapy studies; Viral therapy) of glioblastoma multiformes, 418–425 of multiple myeloma, 403–410 Breast carcinoma, 507, 512, 517–518

Index

Breast cancer cells, 348–349, 721 Bronchioalveolar carcinoma, 325 Burkitt’s lymphoma, 6, 273 Bystander effect, 470 Cancer cells, exploiting defects in, 607–613 selective replication, 610–611 and therapeutic index, 611–613 tumor cell defects, 607–610 Catenins, caveolins, and connexins, 339–340 CD46 receptor, 41 CD155, 740, 747–755, 757, 759 Cell cycle, 539–540 Cell entry, retargeted, and measles virus, 468–470 Central nervous system (CNS) malignancy, 740, 744–745, 747–751, 754–755 Chemo-immunotherapy, 14, 511–513 (see also Chemotherapy; Clinical immunotherapy studies) Chemokines, 333–343, 452 growth factors, 333–343 autocrine circuits, 340–342 catenins, caveolins, and connexins, 339–340 expropriated cytokines, 333–336 matrix metalloproteinases and chemokines, 336–338 mesothelioma, 338–339 virus-induced cytokines and chemokines, 342–343

817

Chemotherapy, detrimental effects of, 14, 511–513 (see also Biological therapeutics; Biotherapy; Clinical immunotherapy studies; Viral therapy) Chondrichthyes, 83 c-jun gene, 48, 606 (see also Genetic stability) Clinical immunotherapy studies, 495–504 (see also Biological therapeutics; Biotherapy; Chemotherapy; Viral therapy) autologous virus modified tumor vaccine, 495–497 effects of repeated vaccinations, 500–501 hypersensitivity responses and prognosis, 503–504 nonresponder patients, 503 phase I, optimization of vaccine composition, 497–498 potentiation of antitumor memory response, 502 specificity of responses, 498–500 turning immunological nonresponders into responders, 501–502 Clostridia, 75, 176 c-myc, 270, 272–274, 398 Colorectal carcinoma, 506, 507 Corynebacteria, 18, 693 Coxsackie-adenovirus receptor (CAR), 56, 63, 64, 180, 746, 756, 768, 789–790 c-ras, 151–156 Creutzfeld–Jakob disease, 75 Cycline-dependent kinases (CDK), 221–223, 238 (see also Cycline-dependent

818

[Cycline-dependent kinases (CDK)] kinases; Double-sided RNA-dependent protein kinases; Janus protein kinases; Protein kinases; Thymidine kinase; Tyrosine kinase inhibitors) Cyclins, 221–223 Cyclooxygenase inhibitors, 231–235, 237 (see also Farnesyl transferase inhibitors; Inhibitors) eicosanoids, 231–233 nonsteriodal antiinflammatory agents, 233–235 Cyclophosphamide (CTX), 55 Cytokines, 161, 333–336, 342–343, 452 expropriated, 333–336 virus-induced, 342–343 Cytomegalovirus (CMV), 52, 802 Cytosine deaminase (CD), 65 Cytotoxicity of enhanced measles virus, 470–471 modulation site-directed mutagenesis, 660 and parvoviruses, 658, 660–661 CyVADIC chemotherapy, 17 (see also Chemotherapy) Delayed hypersensitivity (DTH), 482, 486, 496, 500–504, 511 Delta24 virus, 62, 167 Dormancy studies, 488 Double-sided RNA-dependent protein kinase, 545–546 (see also Cycline-dependent

Index

[Double-sided RNAdependent protein kinase] kinases; Janus protein kinases; Protein kinases; Thymidine kinase; Tyrosine kinase inhibitors) Economic evaluations, 515–516 Eicosanoids, 231–233 Endogenous retrovirus, 34 Endostatin gene, 8 Engineering to improve efficacy of VSV, 613–616 increasing induced antitumor immunity, 614–615 increasing toxicity, 614 retargeting the VSV glycoprotein, 615–616 Env gene, 32, 33, 34 (see also Genetic stability) Enterococcus faecium, 4 Enterovirus, 74 Epidermal growth factor (EGF), 52, 177–178, 225, 231, 238, 269, 326, 347, 355, 356, 422, 454, 469, 799, 803 (see also Fibroblast growth factor; Growth factors; Insulinlike growth factors; Tumor growth factors; Vascular endothelial growth factor) Epstein–Barr virus (EBV), 7, 159, 177, 704, 714 Esb model, 483–484 Escherichia coli, 64, 470, 716 E2F, 781–786 Evaluation of standard therapies, critical, 511–516 Exploiting defects in cancer cells, 607–613 selective replication, 610–611

Index

[Exploiting defects in cancer cells] and therapeutic index, 611–613 tumor cell defects, 607–610 Farnesyl transferase inhibitors, 151–172 (see also Cyclooxygenase inhibitors; Inhibitors) adenoviral oncolysis, 162–168 c-ras, 151–156 [Farnesyl transferase inhibitors,] virus attack/host counterattack, 156–162 Fas ligand, 59 Fibroblast growth factor (FGF), 56 (see also Epidermal growth factor; Growth factors; Insulinlike growth factors; Tumor growth factors; Vascular endothelial growth factor) Flavopiridols, 221–226 cyclins, 221–223 flavopiridols-induced apoptosis, 223–224 inhibitors, 224–226 Friend virus, 32, 33 Fused ‘‘chimeric’’ cells, 19–23 Fusogenic oncolytic herpes simplex viruses, 713–738 construction by insertion of gibbon ape leukemia virus, 721–726 construction through random mutagenesis, 720–721 development for tumor therapy, 716–717 enhancing the potency, 718

819

[Fusogenic oncolytic herpes simplex viruses] infection and replication, overview, 713–715 rationale for using, 718–720 safety, 728 summary 728–729 using both fusion mechanisms, 726–727 G207 mutant virus, 54 Ganciclovir, 614 Gastrointestinal stromal tumor (GIST) cells, 174, 800 gef genes, 5, 155 (see also Genetic stability) Genetic stability, and poliovirus, 766–768 Gibbon ape leukemia virus (GALV), 721–726 (see also Animal tumor models; Animal tumor vaccine; Leukemia) Glioblastoma multiforme, 410–425, 452, 506, 508, 721, 753–754, 805 biotherapy, 418–425 pathogenesis, 410–418 Glioma, and poliovirus recombinants, 739–779 molecular biology and pathogenesis, 740–745 life cycle, 740–743 pathogenesis, 743–745 oncolytic agents, 745–764 tumor-specific virulence, 755–764 viral target tropism, 745–755 safety, 764–768

820

[Glioma, and poliovirus recombinants, 739–779] attenuation of neuropathogenic properties, 764–766 genetic stability, 766–768 Glycoproteins, 615–616, 719 HSV, 719 retargeting VSV, 615–616 GM-CSF gene, 8 (see also Genetic stability) Growth factors, 80, 800 (see also Epidermal growth factor; Fibroblast growth factor; Insulinlike growth factors; Tumor growth factors; Vascular endothelial growth factor) Hematological malignancies, virotherapy of, 466 Hepatitis viruses, 74, 159 Herpes viruses, 51–55, 63, 64, 69, 82, 713–738 fusogenic oncolytic HSV, 713–738 construction by insertion of gibbon ape leukemia virus, 721–726 construction through random mutagenesis, 720–721 development for tumor therapy, 716–717 enhancing the potency, 718 infection and replication, overview, 713–715 rationale for using, 718–720 safety, 728 using both fusion mechanisms, 726–727

Index

[Herpes viruses] simplex, 52, 53, 63, 64, 69, 82, 713–738 Hodgkin’s disease, 6 Hormone-related events in breast and prostate cancers, 343–350 complex interactions, 343–346 observations, 346–350 HPV E7 gene, 8, 160 HSV1 G92A, 167 Human Genome Project, 264 Human herpes virus type 8 (HHV-8), 7, 51 Human immunodeficiency virus (HIV), 6, 75, 263, 615–616 Human leukocyte antigen (HLA), 52, 492 Human papilloma virus (HPV), 8, 159, 160, 284, 608, 781, 782 Human T cell leukemia virus-I (HTLV-I), 7 Hypersensitivity responses and prognosis, 503–504 IL-2, 160, 421, 451, 540, 551, 553, 615, 718 IL-4, 334, 354, 451, 615, 651, 718 IL-6, 334, 401, 403, 404 IL-8, 158, 229, 282, 334 IL-10, 234, 334, 615 IL-12, 8, 160, 234, 279, 334, 402, 421, 423, 615, 718 IL-13, 451 Imatinib mesylate, 172–177 Immune memory, 489, 519–523 and residual tumor cells, 489 Immune reactions, 19–32

Index

Immune system, conditioning, 494, 547 conditioning, 494 role of immune system, 547 Immunoglobulin superfamily (IGSF), 740–743, 746–747, 753, 755 Immunological nonresponders, turning into responders, 501–502 Immunotherapy studies, 495–504 autologous virus modified tumor vaccine, 495–497 effects of repeated vaccinations, 500–501 hypersensitivity responses and prognosis, 503–504 nonresponder patients, 503 phase I, optimization of vaccine composition, 497–498 potentiation of antitumor memory response, 502 specificity of responses, 498–500 turning immunological nonresponders into responders, 501–502 Influenza A virus, 10, 32, 36–40, 69, 575–595 characterization of, 576–577 of the genome, 577 delNS1, 579–580 IFN pathway and the NS1 protein, 580–581 IFN resistant tumors, 583–585 introducing mutations, 578–579 oncolytic reoviruses, 588–591 principle of, 575–576

821

[Influenza A virus] properties of, 586–588 tumor-associated defects, 581–583 in JAK/signal transducer, 581–582 in protein kinase, 582–583 tumor expression, 585–586 Inhibitors (see also Cyclooxygenase inhibitors; Farnesyl transferase inhibitors) farnesyl transferase, 151–172 flavopiridols, 224–226 metalloproteinase, 228–231 molecular, 238–240 of neoangiogenesis, 278–286 Insulinlike growth factor, 240, 327–328, 340, 469, 799 (see also Epidermal growth factor; Fibroblast growth factor; Growth factors; Tumor growth factors; Vascular endothelial growth factor) Intercellular adhesions, 329–330 Interferon (IFN), 152, 279, 486, 487, 492, 497, 510, 537, 540–544, 553, 556, 557, 580–581, 583–585, 597, 598, 603–607, 608, 610–613, 614, 615–617, 651, 656, 692, 702, 705, 800 pathway, 540–544, 580–581 production, 156, 279 resistant tumors, 583–585 VSV sensitivity to, 603–607 Intergenomic recombination, 767–768 Internal ribosome entry sites (IRES), 73, 741–743, 756–762, 765, 766

822

Janus protein kinases (JAK), 40, 45, 161, 173, 239, 581–582 (see also Cyclinedependent kinases; Doublesided RNA-dependent protein kinases; Protein kinases; Thymidine kinase; Tyrosine kinase inhibitors) Kaplan Meier estimates of survival, 697, 699 Kaposi’s sarcoma, 33, 51, 69, 237, 279–280, 334, 416 Kilham rat viruses (KRV), 628, 637, 638, 644, 650, 651 (see also Animal tumor models; Animal tumor vaccine; Minute virus of mice) Leukemia, 2, 6, 7, 20 (see also Gibbon ape leukemia) acute, 6 Life cycle, of poliovirus molecular biology, 740–743 Loss of RB or p53, 781–795 clinical experience with ONYX-015, 789–790 conclusion and future prospects, 790 introduction, 781–784 ONYX-015 and the p53 pathway, 786–789 failure to replicate, 788 replication in tumor cells, 787–788 virus dependency, 784–786 Lymphocytes, 23–25, 31, 640 large, 23, 25, 31, 640 Lymphokine-activated killer (LAK) cells, 19, 30, 84, 266, 353, 424, 455, 804 Lyssa, 2

Index

Major histocompatibility complex (MHC), 52, 67, 82, 159, 636 Malignant melanoma, 17, 506, 508, 509, 677–689, 693–695 and NDV, 677–689 clinical findings, 681, 684 conclusion, 685–686 discussion, 681–685 procedures, 680 rationale, 678–680 and vaccinia viral lysates, 693–695 Matrix metalloproteinases and chemokines, 336–338, 544 Measles virus, 40–42, 459–480 improving oncolytic properties by genetic engineering, 459–480 with enhanced cytotoxicity, 470–471 molecular biology and reverse genetics, 461–465 oncolytic properties, 459–461 perspectives, 471–473 with retargeted cell entry, 468–470 trackable, 467–468 treatment of ovarian cancer, 466–467 virotherapy of hematological malignancies, 466 Mechanism of NDV, 539–547 (see also Newcastle disease virus) cell cycle, 539–540 interaction of proteins, 539–540

Index

[Mechanism of NDV] interferon pathway, 540–544 ras connection, 544–545 role of dsRNA-dependent protein kinase, 545–546 role of immune system, 547 Memory T cells, 489–490, 491–492 characteristics of, 489–490 Mesothelioma, 266, 268, 338–339, 801 Metalloproteinases (see also Protein kinase) and chemokines, 336–338 inhibitors, 228–231 pathophysiology, 228–230 Microvascular tumor bed, 331–333 microvasculature, 331–332 suppressors, 332–333 Minute virus of mice (MVM), 68, 69, 628, 631,634–636, 639–640, 644, 646, 647, 650–652, 655–660 (see also Animal tumor models; Animal tumor vaccine; Kilham rat viruses) Molecular biology and pathogenesis of poliovirus, 740–745 and reverse genetics, 461–465 Molecular oncology, recent developments, 235–241 Moloney virus, 32 Monoclonal antibodies, 286–287, 345, 451 Multiple myeloma, 396–410, 452 biotherapy, 403–410 pathogenesis, 396–403

823

Mutations, introducing, and influenza A virus, 578–579 Mycobacteria, 4 Natural hybridomas, 20, 330–331 formation, 20 Natural killer (NK) cells, 19, 23, 56, 67, 77, 78, 80, 83, 84, 159, 290, 327, 455, 486, 491, 509, 632, 646, 679, 804, 805, 806 Newcastle disease virus (NDV), 6, 8, 10, 11, 12, 13, 19, 30, 32, 34, 36, 40, 42–45, 53, 69, 77, 80, 82, 156, 484, 485, 487, 494, 496–498, 499, 500–510, 523, 533–574, 677–689, 802, 803, 806 breaking tolerance, 494 disease model, 484 future directions, 557–558 introduction, 533–534 and malignant melanoma, 677–689 clinical findings, 681 conclusion, 685–686 discussion, 681–685 procedures, 680 rationale, 678–680 mechanism of, 539–547 cell cycle, 539–540 interaction of proteins, 539–540 interferon pathway, 540–544 ras connection, 544–545 role of dsRNA-dependent protein kinase, 545–546 role of immune system, 547

824

[Newcastle disease virus] oncolytic agent, 537–539 postoncolytic tumor immunity, 551–553 P701, 36, 44 safety, 556–557 73T, 34, 36, 44, 45, 537–539, 549, 553, 802 therapy of human cancer, 547–551 Ulster, 496–498, 802 viral oncolysate vaccines, 553–556 viral replication cycle, 534–536 virion, 534 [Newcastle disease virus] virulence and host specificity, 536–537 Nitroimidazole reductase (NTR), 64 NOD/SCID, 491–492, 493, 538, 584, 586, 589, 590, 591 Non-Hodgkin’s lymphoma (NHL), 466 Nonresponder patients, 503 Nonsteriodal anti-inflammatory agents, 233–235 NRF-1 factor, 749–750 Oligonucleotides (see Antisense oligonucleotides) Oncolytic agents of poliovirus, 745–764 tumor-specific virulence, 755–764 viral target tropism, 745–755 Oncolytic properties, 459–461 ONYX-015, 167, 234, 421, 598–599, 781–795, 802 (see also RB gene)

Index

[ONYX-015] clinical experience with ONYX-015, 789–790 ONYX-015 and the p53 pathway, 786–789 failure to replicate, 788 replication in tumor cells, 787–788 virus dependency, 784–786 OSI-774 erlotinib, 179–180 Ovarian cancer, treatment of, 466–467, 509, 589 Pancreatic carcinoma, 509 Paracrine circuits, 324–427 Paramyxoviridae, 45, 461, 470 Parvoviruses, 68–72, 74, 627–675 conclusion, 661–662 mechanisms of antitumor activity, 642–652 animal models, 646–647 evidence of oncolytic effects, 642–645 immune system and tumor clearance, 649–652 tumor cell targets, 647–459 motivation for therapeutics against cancer, 633–642 failure to signal danger, 635–636 interference with tumor development, 636–642 preimmunity is low, 633–635 perspectives, 657–661 modulation of cytotoxicity through site-directed mutagenesis, 660 targeting specific tumors through P4 modifications, 659–660

Index

[Parvoviruses] transduction of cytotoxic transgenes, 658 vaccination, 658–659 recombinant parvoviruses, pre-clinical studies, 652–657 construction of vectors, 652–653 improved antitumor capacity of transgenes, 653–657 outcome of therapies in humans, 631–633 viral life cycle, 628–631 P53 pathway, 781–795, 802 virus dependency, 784–786 P4, modifications and parvoviruses, 652, 659–660, 653, 659, 660 (see also Parvovirus) Picornaviridae, 74, 740 Platelet-derived growth factor, 239, 800 Polio-rhinovirus recombinants, 72–74 Poliovirus recombinants against malignant glioma, 739–779 introduction, 739–740 molecular biology and pathogenesis, 740–745 life cycle, 740–743 pathogenesis, 743–745 oncolytic agents, 745–764 tumor-specific virulence, 755–764 viral target tropism, 745–755 safety, 764–768 attenuation of neuropathogenic properties, 764–766

825

[Poliovirus recombinants against malignant glioma] genetic stability, 766–768 Poly(A) binding protein (PABP), 741–743 Postoncolytic antitumor immunity, 10–12 (see also Antitumor immune memory) PR8 virus, 16, 17, 18, 30, 38 Prominent targets and molecular inhibitors, 238–240 (see also Inhibitors) Protein expression, and measles virus, 465 (see also Measles virus) Protein kinase C inhibitors, 226–228 Protein kinase (PKR), 38, 50, 60, 181, 545–546, 576, 582–583, 604–607, 609, 798 (see also Cyclinedependent kinases; Doublesided RNA-dependent protein kinases; Janus protein kinases; Thymidine kinase; Tyrosine kinase inhibitors) Proteins, interaction of, 539–540 Pseudomonas aeruginosa, 5 P701, 36, 44 (see also Newcastle disease virus) Rabies vaccine, 2–3 Radiotherapy, 511, 512–513 Rapamycins, As-ODN, and lymphocytes, 322–324, 405 Ras antagonists, 171, 544–545, 802

826

Rat viruses (see Kilham rat viruses) RB gene, oncolytic viruses and dependency, 781–795 (see also Genetic stability) clinical experience, 789–790 conclusion and future prospects, 790 introduction, 781–784 ONYX-015 and the p53 pathway, 786–789 failure to replicate, 788 replication in tumor cells, 787–788 virus dependency, 784–786 Reovirus, 47–49, 588–591 Replicating cancer therapeutics, of VSV, 598–599 (see also Vesicular stomatitis virus) Residual tumor cells and immune memory, 489 Rhabdoviridae RNA virus, 45 Rhinovirus, 74 Risk–benefit ratio, 76 Rubulavirus, 42 Sabin vaccine, 766–767 Safety measures and regulations, 74–77, 556–557 and NVD, 556–557 and poliovirus, 764–768 attenuation of neuropathogenic properties, 764–766 genetic stability, 766–768 SCID/NOD, 491–492, 493, 538, 584, 586, 589, 590, 591, 641 Semliki Forest virus (SFV), 8 Secreted morphogen sonic hedgehog (Shh), 750–751 Serratia, 4

Index

73T, 34, 36, 44, 45, 537–539, 549, 553, 802 (see also Newcastle disease virus) Side effects, and antitumor immune memory, 504–511 (see also Antitumor immune memory) conclusions of survival data, 509–511 five-year survival, 505–508 long-term survival, 508–509 overall median survival, 508 phase II clinical vaccination studies, 504–505 two-year survival, 505 Specificity of responses, 498–500 Standard therapies, critical evaluation of, 511–516 rational re-evaluation, 513–515 Staphylococcus aureus, 4 STAT system, 156, 276, 582–583, 603, 604, 606, 608 Stem cell-like properties of memory T cells, 490 St. Louis virus, 10 Stomach carcinoma, 509 Stroma, activated, 328–329 Stromal cells, 24, 341 Suppressors, and microvascular tumor bed, 332–333 Survivin, 799, 802

Telomerases, 165, 321–322 Telomeres, 321–324 rapamycins, As-ODN, and lymphocytes, 322–324 telomerase, 321–322

Index

Therapeutic index, and VSV, 611–613 (see also Vesicular stomatitis virus) Therapeutics, motivation against cancer, 633–642 (see also Biological therapeutics; Biotherapy; Chemotherapy) failure to signal danger, 635–636 interference with tumor development, 636–642 preimmunity is low, 633–635 Thymidine kinase (TK), 47 (see also Cycline-dependent kinases; Double-sided RNA-dependent protein kinases; Janus protein kinases; Protein kinases; Tyrosine kinase inhibitors) Tissue cultures, 320–321 trypsin, 321 Tolerance to tumor-associated antigens, 482, 492–493 Toxicity, increasing, and VSV, 614 Transgenes (see also Antitumor immune memory) improved antitumor capacity of transgenes, 653–657 transduction of cytotoxic transgenes, 658 Trypsin, 321 Tumor-associated antigens, tolerance, 489, 492–493, 494, 496, 500, 522 Tumor-associated defects, 581–583 (see also Protein kinases) in JAK/signal transducer, 581–582 in protein kinase, 582–583

827

Tumor cell defects, and VSV, 607–610 Tumor cell targets, 647–649 Tumor development, interference with parvoviruses, 636–642 Tumor expression, 585–586 Tumor growth factor (TGF), 83, 177, 178, 269, 273, 277, 278, 286, 340, 355, 805 (see also Epidermal growth factor; Fibroblast growth factor; Growth factors; Insulinlike growth factors; Vascular endothelial growth factor) Tumor-specific virulence, of poliovirus, 755–764 (see also Poliovirus recombinants) Tyrosine kinase inhibitors, 172–180, 271, 281 (see also Cycline-dependent kinases; Double-sided RNAdependent protein kinases; Janus protein kinases; Protein kinases; Thymidine kinase) imatinib mesylate, 172–177 OSI-774 erlotinib, 179–180 ZD1839 gefitnib, 177–179 Ulster NDV, 496–498, 802 (see also Newcastle disease virus) Vaccines, 289–290, 495–498, 500–501, 658–659 autologous virus modified tumor vaccine, 495–497 effects of repeated vaccinations, 500–501

828

[Vaccines] optimization of vaccine composition, 497–498 Vaccinia viral lysates, 49–51, 691–712 discussion, 699–702 general issues, 705–707 ineffectiveness, 702–705 in immunotherapy of melanoma, 693–695 introduction, 623–693 results of stage IIB and III melanoma, 695–699 Vascular endothelial growth factor (VEGF), 269, 274–278, 280–282, 286–289, 324, 331–333, 799, 802 (see also Epidermal growth factor; Fibroblast growth factor; Growth factors; Insulinlike growth factors; Tumor growth factors) Vasculogenesis and angiogenesis, 274–278 Vesicular stomatitis virus (VSV), 45–47, 77, 82, 597–625, 803, 806 biology of, 599–607 not a human pathogen, 602 sensitivity to interferon, 603–607 studies of, 599–602 engineering to improve efficacy, 613–616 increasing induced antitumor immunity, 614–615 increasing toxicity, 614 retargeting the VSV glycoprotein, 615–616 exploiting defects in cancer cells, 607–613

Index

[Vesicular stomatitis virus (VSV)] selective replication, 610–611 and therapeutic index, 611–613 tumor cell defects, 607–610 prospects for future research, 616–618 replicating cancer therapeutics, 598–599 Viral blockade, 263–264 Viral engineering, 167 Viral infections, 1 Viral life cycle, 628–631 Viral oncolysates (VO), 12–19, 24, 29, 156, 553–556, 805 vaccines, 553–556 Viral oncolysis, 36–74, 180–182 adenoviruses, 55–68 herpes viruses, 51–55 influenza virus, 36–40 measles virus, 40–42 Newcastle disease virus, 42–45 parvoviruses, 68–72 polio-rhinovirus recombinants, 72–74 recent developments, 180–182 reovirus, 47–49 vaccinia virus, 49–51 vesicular stomatitis virus, 45–47 Viral replication cycle, 534–536 Viral target tropism, and poliovirus, 745–755 Viral therapy of human cancers, progressive development, 1–148, 167, 466, 806 (see also Biological therapeutics; Biotherapy;

Index

[Viral therapy of human cancers] Chemotherapy; Clinical immunotherapy studies) afterthoughts, 78–84 future, 77 history of, 1–6, 32–36 early, 1–6 more recent, 32–36 immune reactions, 19–32 mice to man, 9–10 postoncolytic antitumor immunity, 10–12 safety measures and regulations, 74–77 viral oncolysates, 12–19 viral oncolysis, 36–74 adenoviruses, 55–68 herpes viruses, 51–55 influenza virus, 36–40 measles virus, 40–42 Newcastle disease virus, 42–45 parvoviruses, 68–72 polio-rhinovirus recombinants, 72–74 reovirus, 47–49 vaccinia virus, 49–51 vesicular stomatitis virus, 45–47

829

[Viral therapy of human cancers] viruses interact, 6–9 Virion, 534 Virotherapy of hematological malignancies, 466, 806 Virulence and host specificity, 536–537 Virusarten, 2 Virus attack/host counterattack, 156–162 Viruses, interaction of, 6–9 Virus therapy, 3 Western equine encephalitis (WEEE) viruses, 10 Xenografts, 324–331, 345, 350–357, 763, 764 activated stroma, 328–329 insulinlike growth factor-R, 327–328 intercellular adhesions, 329–330 miscellaneous agents tested, 350–357 natural hybridomas, 330–331 natural killer cells, 327 paracrine circuits, 324–427 ZD1839 gefitnib, 177–179

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Viral Therapy of Cancer

Drug Resistance in Oncology (Basic and Clinical Oncology)

Manual of Clinical Oncology

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Chronic Lymphoid Leukemias, Second Edition, (Basic and Clinical Oncology)

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Basic Radiation Oncology

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